Practices of Seudat Purim
- When one has the Seudah, one should have intent that one is eating the meal in order to fulfill the mitzvah of Seudat Purim.
- The meal should be eaten with friends and family. 
When should one eat Seudat Purim?
- Many Ashkenazim have the minhag to eat the meal after mincha but they should be careful to have majority of the meal during the day, while many Sephardim have the minhag to eat the meal in the morning. Some have a minhag to eat a small meal the night of Purim. 
- The mitzvah of Seudat Purim is during the day and not the night, yet one should have simcha and a small meal at night (and make the meal of the day greater).  If Purim falls out on Motzei Shabbat and Sunday, having Seudat Shelishit isn’t considered as having a small meal during the night of Purim. Rather, one should have a special meal for the sake of Purim. 
- If one began the meal on Purim and ate past nightfall, one should still mention Al HaNissim in Birkat HaMazon  unless one already said Maariv, in which case one shouldn’t say Al HaNissim. Some say that one can say it even after davening Maariv. 
- If purim falls on a Friday a person should have the meal in the morning but if he didn't he can have it after midday (Chatzot) until the beginning of the tenth halachic hour (which is a half hour before Mincha Ketana). After the fact if he didn't have it until the end of the day he should still have the meal then.
What should one eat at Seudat Purim?
- Many poskim hold that one should eat bread and meat in the meal.
If one forgot Al HaNissim
- If one forgot Al HaNissim in Benching, one doesn’t repeat benching. However, if one remembers that he forgot Al HaNissim while still benching one should add it in the Harachaman’s by saying Harachaman Hu Yaaseh Lanu Nissim and continue with Al HaNissim. 
Drinking on Purim
- The mitzvah to drink only applies to wine. Although most Rishonim seem to require one to reach a level of drunkenness , most later authorities, Ashkenazic and Sephardic, hold that one should only drink a little more than what one is accustomed to drink and then sleep (see note for procedure).  All agree that if one going to end up violating or degrading any halacha such as Birkat HaMazon, one should not get drunk. 
- If one’s parent tells one not to drink on purim one should listen to them and only drink a little more than usual. 
- Women are not required to drink as much. One cup or less is sufficient. 
- If one unintentionally causes minor damages as a result of celebrating purim, one is exempt from paying for the damages. 
Regarding reciting brachot and davening after drinking see Avoiding Davening After Drinking Intoxicating Beverages.
- Rama and S”A 695:1
- Shulchan Aruch 60:4 rules like the Rishonim who say that Mitzvot need kavana. Mishna Brurah 60:9 quotes the Gra who says that mitzvot derabbanan also need kavana, while the Magen Avraham disagrees. It’s clear from S”A 696:7 that eating Seudat Purim is MeDivrei Kabbalah (which in some respects is similar to a Deoritta). Therefore, Pri Megadim (M”Z 695:1) writes that one should have intent that one is eating the meal to fulfill the mitzvah of Seudat Purim. Mishna Brurah 695:4 quotes this as halacha.
- Eliyah Rabba 695:4 writes that the meal should be eaten with family and friends in order to have Simcha. Mishna Brurah 695:9 quotes this and adds that it should be a Simcha of Torah. See Gemara Shabbat 88a which says that Purim was a Kabbalah MeAhava of the Torah.
- Rama 695:2
- Rama 695:2 writes that the minhag is to eat the meal after mincha, but one should ensure that majority of the meal is eaten during the day. Rabbi Willig (“Practical Laws of Observance of Purim”, min 41-2) explained that the Rama means that the primary parts of the meal such as the bread, meat, and wine should be consumed during the day. Shalmei Todah (pg 317) also explains the Rama this way.
- However, the Maaseh Rav of the Gra (#248) recommends eating it in the morning. (The Maaseh Rav says that the Gra started his seuda after 'tefilah'. Some learn that this means after mincha, which would be like the first opinion.) Kaf HaChaim 695:23 quotes kabbalistic reasons for eating Seudat Purim in the morning. Torat Hamoadim 11:6 agrees and adds that this was the practice of his father, Rav Ovadia Yosef.
- Shulchan Aruch 695:1 writes that one doesn’t fulfill one’s obligation by eating a nighttime meal. The Rama adds that at night one should have a small meal. Pri Megadim E”A 695:6 presents different minhagim about having meat at the nighttime meal.
- Shulchan Aruch and Rama 695:1, Mishna Brurah 695:3
- Mishna Brurah 695:3
- Shulchan Aruch and Rama 695:3. Or Letzion 4:60:4 writes that as long as one ate a kezayit by day even if the meal continued into the night one can recite Al Hanissim in Birchat Hamazon. Even though the Ben Ish Chai Shana Rishona Chukat 22 wrote that we don't mention Al Hanissim in Birchat Hamazon if it extended into the night, the Or Letzion writes that we follow Shulchan Aruch and Chida. He adds that this was the ruling of Rav Ezra Attiya. Yachava Daat 3:55, Yalkut Yosef (5764, Seudat Purim no. 5), Yalkut Yosef (Bet Yosef edition, 5776, p. 221 695:9), and Torat Hamoadim 11:5 agree.
- Mishna Brurah 695:16
- Rama 695:2 writes that if Purim is on Friday one should have the meal before Chatzot in honor of Shabbat. Mishna Brurah 695:10, Or Letzion 4:60:1, Torat Hamoadim 11:6, and Yalkut Yosef (Bet Yosef edition, 5776, p. 220, 695:7) agree. Mishna Brurah 695:10 writes that after the fact one can still have the meal afterwards.
- Torat Hamoadim 11:6 adds that if one didn't have the meal before Chatzot one should do so before a half hour before Mincha Ketana and if one didn't do so one can still have the meal until the end of the day.
- Rambam Megillah 2:15 writes that the meal should consist of meat and wine. The Magen Avraham 696:15 questions the need for meat. Nonetheless, many poskim including Kaf HaChaim 695:6, Chazon Ovadyah pg 173, and Nitei Gavriel 71:3 agree that one should have meat. Shaar HaTziyun 695:12 implies it’s an obligation. Kovetz MeBet Levi (5758, vol 13, pg 32) writes that having meat is not MeAkev.
- The Birkei Yosef 695:1-3 and Magen Avraham 695:9 write that there’s no obligation to eat bread. However, Aruch HaShulchan 695:7, 12 argues that mishteh is defined by bread. Chayei Adam 155:30 says the same. Nitei Gavriel 71:1 and Yalkut Yosef 695:4 write that one should be strict to have bread. Or Letzion 4:60:2 agrees that essentially one doesn't need bread but one should be strict to have it. Mishna Brurah makes no mention of it except in Shaar HaTziyun 695:4 where he leaves it as a dispute.
- Mishna Brurah 695:15
- Gemara Megillah 7b. Rambam (Laws of Megillah 2:15), Rif Megillah 3a in Dapei HaRif, Rosh Megillah Perek 1 Siman 8, Tur Orach Chayim 695:1 seem to require one to reach a level of drunkenness. See Emek Bracha (p. 126) who quotes Rav Yisrael Salanter as explaining that one is obligated to continue to drink and is only exempt once one reaches a level of drunkenness that one doesn't realize between "blessed is Mordechai" and "cursed is Haman".
- The Bet Yosef 695:1 quotes the Orchot Chaim who writes that it’s forbidden to get drunk; rather the mitzvah is to drink a little more than one is accustomed to drink. Darkei Moshe HaAruch 695:2 quotes the Mahariv as saying that one should drink, and then sleep so that one doesn’t know the difference between Arur Haman and Baruch Mordechai. Rama 695:2 combines the Orchot Chaim and Mahariv saying that one should drink more than one is accustomed to drink and then sleep.
- Mishna Brurah 695:5 explicitly rules that this is the accepted halacha. This was also the minhag of Rav Shlomo Zalman (Halichot Shlomo pg 343 note 78). Rav Hershel Schachter in a shiur on yutorah.org (“Inyanei Purim”, min 81-83) explained that one should drink a little more than one is accustomed to, and then fall asleep after the meal. Rabbi Willig (min 42-6), however, explained that according to the Rama one should drink a little, sleep, and then have the Seudah, and drink a little in the meal. Yalkut Yosef 695:14 rules like the Orchot Chaim and makes no mention of sleeping. Rav Mordechai Eliyahu in MaAmer Mordechai 64:36 who seems to agree.
- Rashi Megillah 7b s.v. LeIvsumei and Rambam 2:15 specify wine and not other intoxicating drinks. Kaf HaChaim 695:6 and Nitei Gavriel 73:2 codify this as halacha. Rabbi Willig (min 44-5) rules that it’s prohibited to have intoxicating drinks other than wine on Purim or any day of the year. However, Shalmei Todah (pg 326) quotes Rav Nissim Karlitz saying that it’s not MeAkev to have wine specifically. Rav Shlomo Zalman (Halichot Shlomo pg 342, note 76) writes that grape juice does not suffice.
- The Chaye Adam 155:30 writes that if one knows that getting drunk will cause one to degrade fulfilling a mitzvah such as making Brachot, Birkat HaMazon, or Maariv, one shouldn’t get drunk. This is quoted by the Beiur Halacha s.v. Ad and Kaf HaChaim 695:17. This is supported by the Mieri (Megillah 7b) who writes that we’re not commanded to have happiness of vanity and frivolity, rather one should have happiness that leads to Ahavat Hashem and a desire to thank Him for the miracles he did for us.
- The Roshei Yeshiva of Yeshiva University signed a letter (dated Feb 26 2015) stating that one should fulfill the mitzvah of drinking according to the Rama. They emphasize that it is incumbent upon the community to ensure that that individuals avoid the risks of intoxication and Chilul Hashem which could result from it.
- Halichot Shlomo 19:25
- Sh"t Rivevot Ephraim 1:458, Moadim Uzmanim 2:190
- M.B 6595: 5