I had a filling in one of my top back teeth. what foods should i avoid?

Depends...: Unfortunately, without knowing what material was used for the filling, it is impossible to answer to help: some requires no time to be its full strength, while others may take 24-48 hours. It also depends on the size of the fill in relation to the remaining tooth structure: your dentist may want you to be careful chewing hard or "doughy" food until a crown is placed, if the tooth is weak, too.