Gemara

Beraisa #1: "V'Somachta b'Chagecha" - one must make his household rejoice on the festival.

Question: How does he make them rejoice?

Answer #1: He gives to them wine.

Answer #2 (R. Yehudah): He gives to men what makes them rejoice, and to women what makes them rejoice.

Question: Wine makes men rejoice; what makes women rejoice?

Answer (Rav Yosef - Beraisa #2): Women in Bavel rejoice over colored clothing; women in Eretz Yisrael rejoice over ironed linen clothing.

Beraisa #3 - R. Yehudah ben Bava: When the Mikdash stands, one fulfills Simchah only by eating (Kodesh) meat - "V'Zovachta Shelamim...V'Somachta";

Nowadays Simchah is only with wine - "V'Yayin Yesamach Levav Enosh".

Rishonim

The Rif and Rosh bring Beraisa #1 and Beraisa #2.

Rambam (Hilchos Yom Tov 6:17-18): One is obligated to be happy on the seven days of Pesach, the eight days of Sukos and all Yomim Tovim. He, his wife, his children and all his entire entourage must rejoice - "V'Somachta b'Chagecha (Atah u'Vincha u'Vitecha v'Avdecha v'Amasecha)".

Mishnah Berurah (OC 529:15-16): The Mitzvah mid'Oraisa of Simchah also applies to women. There is a Mitzvah of Simchah on Chol ha'Mo'ed, but one need not honor it like Yom Tov (see Sha'ar ha'Tziyon 530:4).

Rambam (ibid.): Even though the verse refers to Shelamim, it also encompasses rejoicing in things that delight men, women and children.

Sefas Emes (Yoma 3a DH b'Tosfos): The Rambam (Chagigah 1:1,3) holds that the Mitzvah of Simchah of eating Shelamim must be fulfilled once during the Regel. Nevertheless, the Mitzvah of Simchah of nice clothes and wine applies the entire Regel. Tosfos (Yoma 3a DH Pazer) holds that there is a Mitzvah to eat Shalmei Simchah every day of the Regel. Whenever this cannot be fulfilled, one fulfills Simchah through nice clothes and wine.

Ri Korkus (Chagigah 1:4): The Rambam holds that Simchah of eating Shelamim applies every day of the Regel.

Rambam (ibid.): One gives parched grain, nuts and special foods to children. One buys nice clothing and ornaments for women according to his means. Men delight in meat and wine; these are essential for Simchah.

Question (Beis Yosef OC 529 DH Kosav and DH u'Mah she'Chosav ha'Ketanim): Why does the Rambam say that men delight in meat - the Gemara says that nowadays, Simchah is only through wine! Also, the Gemara did not say that parched grain and nuts delight children, just that it keeps them awake!

Answer #1 (Yam Shel Shlomo Beitzah 2:5, cited by Gilyon ha'Shas): At all times, meat is necessary for Simchah. The Gemara teaches that when one eats Shelamim, this suffices for Simchah; nowadays that we cannot eat Shelamim, we also need wine. The Tosefta (Pesachim 10:3) says that children delight in what is appropriate for them. Presumably, this refers to parched grain and nuts.

Answer #2 (Bach DH Kosav): There are four Arvei Yomim Tovim when everyone wants beef (Chulin 83a. Bach also cites Shabbos 118b to say that one makes Shabbos pleasurable through 'Basar Shamen (fatty meat)'; our text says instead 'Roshei Shumin (heads of garlic)'.) Nowadays, the primary Simchah is wine; no verse says that Chulin meat gives Simchah. Surely, parched grain and nuts keep children awake because it delights them!

Rambam (ibid.): One must also give food to converts, orphans, widows and other poor people. Hash-m despises one who rejoices with his family but refuses to give to the poor.

Source: "V'Somachta...veha'Ger veha'Yasom veha'Almanah" (Devarim 16:14).

Rambam (ibid.): Drunkenness and frivolity is not a Mitzvah, rather, Simchah that has Avodas Hash-m.

Tur (529): Truly pious people praise Hash-m even more at the time of their Simchah for making them happy.

Poskim

Shulchan Aruch (OC 529:2): One must rejoice on the festival; he, his wife, his children and his entire entourage.

Kaf ha'Chayim (38): One should not discuss things that will upset him, e.g. the death of beloved ones, just like on Shabbos.

Shulchan Aruch (ibid.): One gives parched and grain to children to make them rejoice; one buys nice clothing and ornaments for women according to his means.

Kaf ha'Chayim (40): If one cannot afford a new garment for his wife, he should at least get her new shoes.

Shulchan Aruch (ibid.): One must also give food to converts, orphans, widows and other poor people.

Kaf ha'Chayim (42): One should strive to give to people who are bashful to take openly, in particular if they are learned.

Shulchan Aruch (ibid.): Drunkenness and frivolity is not a Mitzvah.

Kaf ha'Chayim (45): The Magid warned the Beis Yosef to minimize eating and drinking even on Shabbos and Yom Tov, just he should eat l'Shem Mitzvah.