There are tons of different things that can be fed, most fruits and vegetable, all sorts of things like bloodworms, krill and on and on, i suggest going down to the food section of this board and reading some posts. Then you will be set
There a lot of things that should not be fed, so if you are unsure ask first. Don't feed anything that has more than trace amounts of added sugar salt or spices, and don't feed mammilian meats (like chicken or beef), since goldfish cannot digest the type of fat they contain.