At the very least-two cooked dishes:
Even one who cannot afford to buy many varieties of foods for Shabbos, nonetheless it is proper to beware to have at least two cooked foods [by each meal]. [This applies for the first two Shabbos meals but not for the third meal, in which case having less than two dishes suffices. If one generally has two cooked dishes for his weekday meal then he is to increase on Shabbos and have three cooked dishes. If one is accustomed to have three cooked dishes during the week, he is to have four on Shabbos.]
 Admur 242:7; M”A 242:1; Zohar 1:48; M”B 242:2
 Lit. Tavshilin. This refers to two cooked foods. [see Peri Megadim 242:1; 527:12] As for the definition of cooked foods in this regard the Peri Megadim [242 A”A 1] refers the reader to chapter 627:3-4 [Admur 11-12] in which the definition of Tavshilin, cooked foods, is discussed regarding the Mitzvah of Eruv Tavshilin. There cooked foods are defined as follows: Any food which is cooked, fried, baked, pickled and is eaten together with bread is defined as a cooked food. Thus, one may use meat, fish or eggs. A raw food is invalid.
 Nimukeiy Orach Chaim 242
 Kaf Hachaim 242:9