You probably know instinctively that eating too much packaged food is bad for you. Well fresh food is good for your fish too. Fish food makes up about 50% of my fish's diets because it contains the vitamins and minerals they need and is a good balanced diet. I store it in the freezer to keep it fresh.
Depending on what fish you have they will appreciate fresh vegetables and also meats. Some fish will appreciate a small amount of cooked egg white - tiny slivers cut off with the knife. Do not use the yolk unless feeding tiny fry because it will disintegrate into particles adult fish cannot eat and then rot the water.
Meat can be fed as well. A small shellfish such as might be found in marinara mix can be dropped in and left until the fish eat all of it. Tiny slivers of raw beef, chicken, lamb or fish are also suitable. My fish won't eat pork for some reason. Cooked prawns work well too, halve them and then slice into little half circles and drop those in. Remove any uneaten egg, meat or fish after about three or four hours. After this time the fish usually lose interest and it stays there until it rots. It can be left longer if you have shrimp in the tank; they will love you for leaving it there.
Vegetables are one of the best things to feed fish. Leafy greens are appreciated by anything herbivorous; most livebearers, particularly platies, enjoy them. So do brsitlenose catfish, corys, and most other fish will nibble them. Scalded lettuce leaves work well - pour boiling water over a lettuce leaf, let it sit until it cools, drop it in the tank. Do not use the outer leaves and wash the leaf first. Celery works if shredded or the leaves are used. Do not use cabbage, brussels sprouts or anything with a strong smell such as onion, leek or shallot. Garlic can be used as a fish attractant but should be used sparingly and saved for medication. If using large vegies such as carrot, pumpkin or potato shred them first as fish will not attack hard objects that don't fit in their mouths.
I wouldn't use bread, it falls apart and rots the water. In ponds it works better with inverts etc. to clean it up.