Non-established [meals] are eaten and drunk outside of the sukkah.

Casual eating and drinking are permitted outside the sukkah. How much is considered casual eating? R. Joseph said, [The volume of] two or three eggs. Abaye said to him: But sometimes this suffices for [a whole meal for] a man, and then it would be a set meal? ... Rather Abaye said: as much as a student and then goes into the learning session.

How much is this amount of food? The size of an beitzah (egg).

(2) We eat and drink... in the Sukkah all seven days, both day and night... However, one may eat an insubstantial meal outside of the Sukkah. And how much is an insubstantial meal? Approximately an egg's worth of a loaf of bread. And it is permitted to drink water and wine and eat fruit even if he made it his meal (own opinion) outside of the Sukkah. And he who is stringent upon himself, and will not drink even water outside of the Sukkah, he is praised. And a dish made of the five species [of grain], if he makes it his meal, it considered a proper meal and requires a Sukkah.

What else can you eat outside the Sukkah?

Rav Judah said in the name of Shmuel: The blessing is recited over] the lulav for seven [days] and over the Sukkah for only on one day. What is the reason? In the case of the lulav where the nights interrupt the days, each day is a separate commandment; in the case of the Sukkah where the nights do not interrupt the days, all seven days are regarded as one long day. Rabbah b. Bar Hana said in the name of R. Yohanan: [The blessing is recited over] the Sukkah for seven days and over the lulav for one day. What is the reason? For the Sukkah which is a Biblical commandment [the blessing must be recited all] seven [days]; in the case of the lulav which is only a rabbinical commandment [a blessing on] one day suffices.

What exactly did Rabbi Yochanan mean?

However, how do we hold?

Only recite the bracha if you eat a k'beitzah of bread in the sukkah.

Mishnah: Messengers to do a mitzvah are exempt from sukkah. The sick and their attendants are exempt from sukkah. Gemara: From where are these words? As our rabbis taught: (Deuteronomy 6:7) "in your sitting in your house" exempts one involved in a mitzvah.

Our rabbis taught: Day travelers are exempt from the sukkah during day but are obligated at night. Night travelers are exempt from the sukkah at night, but are obligated during the day. Travelers by day and night are exempt both day an night. Those who are going to perform a mitzvah are exempt both by day and by night.

One last exemption from the Sukkah-

All seven days [of the festival] a man must make the sukkah his permanent residence and his house his temporary residence. If rain fell, when is one permitted to leave it? When the porridge becomes spoiled. They made a parable. To what can this be compared? To a slave who comes to fill the cup for his master, and he poured a pitcher over his face.

Our rabbis taught, If he was eating in the sukkah, and rain fell, and he went down from [the sukkah], they do not trouble him to return there until he has finished his meal. ;