Eating and drinking in a Sukkah:
One is only required to eat a set meal inside a Sukkah. However it is permitted to eat a snack outside the Sukkah. The definition of a snack is a Kibeitza or less of bread or Mezonos and any amount of any other food. This applies even if one makes a set meal on other foods nevertheless he is not required to eat them in a Sukkah. Thus one is only required to eat in the Sukkah if he is eating more than a Kibeitza of bread or Mezonos [within Kdei Achilas Pras]. However it is praiseworthy for one to be stringent upon himself to not drink even water outside the Sukkah.
Must one eat a meal of Hamotzi or Mezonos in the Sukkah every day? There is no maximum or minimum amount of meals that one must eat in the Sukkah. Thus if one desires to eat only foods that are not obligated to be eaten in a Sukkah throughout Sukkahs, he may do so. However this only applies on Chol Hamoed, however on Shabbos and Yom Tov, since according to some opinions one is obligated to eat a Kibeitza of bread for the Shabbos and Yom Tov meal, therefore he must eat these meals in the Sukkah. Furthermore, on the first night of Sukkos, according to all opinions, one must eat at least a Kezayis of bread in the Sukkah. This applies even if it is raining on the first night, although in such a case he is not to say a blessing of Leishev Bassukah. [However the custom of Chassidim is to always recite the blessing.] On the second night of Sukkos in the Diaspora one is not required to eat a Kezayis in the Sukkah if it is raining, although one who desires to be stringent he may do so.
Drinking inside the Sukkah: One may drink all beverages outside the Sukkah including wine. One may drink even more than a Revius. However it is praiseworthy for one to be stringent upon himself to not drink even water outside the Sukkah. This allowance however only applies by a regular drink however to settle oneself down on a beverage such as wine or beer or mead, this must be done in the Sukkah.
Drinking wine and other significant beverages:
Settling oneself over the beverage: One who settles himself down to drink wine, or other beverage of significance of which is it is common to settle oneself upon, is obligated to drink it in the Sukkah. However the blessing of Leisheiv Basukkah is not said upon drinking it, [with exception to Kiddush and Havdala in which it is said].
Due to this, that no blessing is said, it is proper not to drink wine, or other significant beverages, in a settling manner in a Sukkah which one has not, and does not plan to, say in it Leishiev Basukkah that day. [Hence when invited to someone else’s Sukkah to settle with him and drink wine, one is to eat a Kebeitza of Mezonos in order so the blessing of Leisheiv Basukkah cover the wine.] However when eating in a Sukkah that one has said Leisheiv that day, or plans on doing so, then there is no need to refrain from drinking the wine, as it is already included in the blessing of Leishev which was or will be said that day.
Drinking the beverage casually: It is permitted from the letter of the law to drink wine or other significant beverages in an unsettling manner outside of the Sukkah. This applies even if one drinks a lot more than a Revius of the beverage. However one is stringent to not even drink water outside the Sukkah is blessed.
Summary-Eating outside of the Sukkah:
According to the letter of the law one is only required to eat in the Sukkah if he is eating more than a Kibeitza of bread or Mezonos [within Kdei Achilas Pras]. All foods which do not carry the blessing of Mezonos or Hamotzi may be eaten outside the Sukkah without limit, even if one sets a meal over those foods. However one who is stringent to eat also these foods in the Sukkah, is praised. Our Minhag is not to eat anything outside the Sukkah, including even water.
 The reason: The reason one may eat up to a Kibeitza of Mezonos and bread is because this is the amount of food a person would regularly eat outside his home and a Kibeitza is the amount of food a person would eat in one shot outside his home, as the mouth cannot hold more than a Kibeitza. [ibid]
 The reason: The reason for this is because these foods are not considered like a mere snack of bread. [ibid]
 Bikureiy Yaakov 639/13
 The reason: As the Mitzvah is not to eat food in the Sukkah but rather that if one desires to eat a meal then he is to eat it in the Sukkah. [639/17]
 The reason: As it is forbidden to eat more than a Kibeitza outside the Sukkah. [639/17] However according to the other opinions, that one is only obligated to eat a Kezayis of bread during the Shabbos and Yom Tov meals, then one is not required to eat any Shabbos or Yom Tov meal in the Sukkah. [639/19] Furthermore even according to the first opinion one may eat only a Kezayis in the Sukkah and then eat another Kezayis and the rest of the meal out of the Sukkah. [639/17]
 The reason: As even according to the opinion which holds that one need only eat a Kezayis for Shabbos meals they learn from a Gezeiras Shava from Pesach that just like on the night of the 15th of Nissan one is required to eat a Kezayis of Matzah, similarly on the night of the 15th of Tishreiy one is required to eat a Kezayis of bread in the Sukkah. [639/19]
 This matter is disputed between the two opinions mentioned above. The first opinion learns the verse from Pesach to teach us that one must eat a Kezayis of bread in the Sukkah on the first night even in the rain. [639/17] However according to the second opinion the verse only teaches us that one must eat a Kezayis in the Sukkah on the first night when it is not raining. Practically we rule like the first opinion although a blessing is not recited. [639/19]
 639/12; so rules also M”B 639/13 Biur Halacha “Veyayin”; Kitzur SH”A 135/7
Other Opinions: It is evident from the Rama that it is permitted to drink wine and any other beverage outside the Sukkah even if one settles himself over it. [Rama 639/2; M”B 639/13]
Proof for opinion of Admur: The Gemara [Sukkah 28b] says that one is obligated to eat, drink, and sleep in the Sukkah. This ruling is brought down in the Shulchan Aruch 639/2 and in Admur 639/4. Now, if there are no drinks that are obligated to be drunk in the Sukkah then what is the meaning behind this ruling regarding drinking. Hence we must conclude that significant beverages which one settles on is obligated to be drunk inside the Sukkah. [Biur Halacha “Veyayin”]
 639/12 and 15
The reason: as A) It is already exempted within the blessing of Leisheiv which was said, or will be said, in that same Sukkah over Mezonos or Hamoitzi. [639/12] and furthermore B) Even in a Sukkah where one does not plan on eating Mezonos or Hamoitzi there, and one has not yet done so, the blessing of Leisheiv should not be said merely over drinking the wine, despite that it is said on sleeping or spending time there, as there are opinions [see above footnote] which question whether a blessing of Leisheiv is to be said over the wine. [639/15]
 As will be explained next.
Other Opinions: The Mishneh Berurah [639/13] and Kitzur SHU”A [135/7] rule that although one is not to say the blessing of Leisheive Basukkah over drinking wine in a settling manner, nevertheless in order to fulfill the obligation like all opinions one is not to settle himself over wine or other significant beverage unless he drinks it within a meal or directly after eating a Kebeitza of Mezonos. [This implies that the M”B/Kitzur in essence rules that wine may require a Leisheiv Basukkah even when drunk in the same Sukkah that one has already said Leisheiv on that day, unlike the ruling of Admur in 639/12, hence he rules that one is to only drink it within a meal and not simply within a Sukkah that Leisheiv has or will be said in, as rules Admur. Possibly the reason for this ruling is because he views wine similar to bread or Mezonos which are significant on their own and are not secondary to any previous blessings said.]
 So rules Admur 639/12. However the Biur Halacha 639 “Yayin” he brings the Ritva which rules that a Revius is already defined as “settling down to drink”. Clearly Admur does not accept the amount of liquid consumed as the measuring factor in the definition of “settling”. Rather one must say settling refers to its simple meaning of spending time over the drink.