The Sages ordained that kiddush be made at the place of the meal (“be-makom se’uda”), for Scripture states: “Call Shabbat ‘delight’” (Yeshayahu 58:13), teaching us that specifically where one delights in Shabbat with bread or pastries he must proclaim Shabbat, i.e., make kiddush. This allows us to reveal the special nature of Shabbat, whose meals are a direct continuation of the mitzva of Zakhor. The proclamation of holiness and the delight with meals complement each other. If one did not eat where he made kiddush, he did not fulfill the mitzva, and he must make kiddush again where he eats. This law applies equally to kiddush by day and by night.
There were some Torah giants who were personally stringent, and insisted on eating their actual Shabbat meal where they made kiddush. This was the custom of the Vilna Gaon. However, the law requires only that one eat a kezayit of bread or mezonot where one makes kiddush. This is sufficient to fulfill the obligation of kiddush. Afterward, one may eat the meal elsewhere. According to the Ge’onim, if there is no mezonot food where one is making kiddush, he may drink a revi’it of wine instead, since wine is also nutritious and filling. If necessary, one may rely upon them. However, at night when the obligation of kiddush is of Torah origin, the person making kiddush should be careful to drink a revi’it in addition to the melo lugmav that he must drink to fulfill the obligation of kiddush. The rest of the listeners need only drink a revi’it (SA 273:5; MB 273:25, 27; SHT 29).
However, if one heard kiddush at the synagogue but only drank a bit of juice and had less than a kezayit of mezonot, he has not fulfilled his obligation of kiddush. Not only that, but he has transgressed the rabbinic prohibition against eating and drinking before kiddush; for since he did not fulfill his obligation, it turns out that he ate and drank before kiddush.
The Rishonim discuss three different parameters for how far away one may go and still be considered eating “at the place of the meal”:
1) Anywhere within the same room is acceptable, even if one place is not visible to another in the same room (Rambam; Tosafot; Rosh).
2) As long as the person making kiddush can see the place where the meal will be eaten, even if that place is in a different home or yard, it is acceptable (R. Sar Shalom).
3) If, while making kiddush, the person had in mind to move to another room in the same building, it is acceptable (R. Nissim Gaon).
Ideally, one should make kiddush at the actual place of the meal. When this is difficult, one may make kiddush anywhere that two of the three criteria mentioned above are met. For example, if one needs to eat in a different room, it is preferable that he have that in mind during kiddush, and that he make kiddush from a vantage point where he can see the place where he is planning to eat. If there is really no choice, one can rely on any one of the three criteria being met (SA 273:1; MB and SHT ad loc.).
Ideally, one should not wait between making kiddush and eating. Similarly, one should not go somewhere after kiddush before eating, even if he intends to return and eat where he made kiddush. Be-di’avad, if he waited for a short time or left briefly, his kiddush still counts. However, if he waited more than 72 minutes and intended to separate kiddush and the meal, then he has “lost” his kiddush and he must make it again (Rema 273:3; MB ad loc. 12; BHL s.v. “le-altar”; Kaf Ha-ĥayim ad loc. 29; Tzitz Eliezer 11:26; Yalkut Yosef 273:15; SSK 54, nn. 46-47).