77:14 Whether by night or by day, Kiddush is only made in the place where the meal is held. This is based on Isaiah 58:13, “You shall call Shabbos a delight,” which the Sages interpreted to mean that the place where you “call” Shabbos, i.e., where Kiddush is recited, should be the place where you “delight.” If one made Kiddush in one house and ate in another, even if it was his intention to do so when making Kiddush, he does not fulfill his obligation in Kiddush. (One need not repeat Kiddush if he can see the place of the meal from the place where Kiddush was said – Mishnah Brurah 273:6.) One must eat immediately after Kiddush; if one does not eat immediately after Kiddush, he does not fulfill his obligation. (If the delay was unavoidable, Kiddush need not be repeated - Mishnah Brurah 273:13.) If a person is not yet ready to eat lunch, he can make Kiddush and have some cake (at least a k’zayis - an olive-sized portion of approximately 1.1 ounces – MB 273:21). In this case, one must drink at least a revi’is of wine so that he may recite a concluding bracha. All this may even be done before Musaf if one is feeling weak. If a mohel, who needs to make a bracha over the wine for a bris, has not yet made Kiddush, he should drink a cheek-full plus a revi’is.
77:15 One is permitted to eat a little in between Shacharis and Musaf. This snack may be an egg-sized portion of bread (a “k’beitzah” – approximately 2.2 ounces), but not larger. (One may eat more if he is truly weak from hunger – MB 286:9.) One may eat as large a quantity of fruit as necessary to fill himself up so long as he made Kiddush and drank a cheek-full plus a revi’is of wine. When necessary, we rely on a cheek-full plus a revi’is of wine to fulfill the obligation of making Kiddush in the place of the meal. (One should only rely upon this leniency in pressing circumstances – MB 273:25). Alternately, one can drink a revi’is of wine and eat a k’zayis (see above) of one of the five species of grain.