Go to the fresh seafood section of your grocery store and see if they have a pre-mix makeup [usually done to mix up a seafood salad, but, in this case great for fish food]. The one I get is usually musels, shrimp, scallops, squid, lobster, clams. If they have this, ask them to give you a handful [or 2, depending on your size fish and # of tank occupants]. If they don't have this, then ask them to give you a mix of whatever stuff you want to feed your fish--again amounting to about a handful, or, if you have big agressive eating fish, then 2 handfuls.
Take this home and food process it to the chunk size you think is best for your particular fish. If you have herbivores, then add Seaweed Selects or Nori, or, if you want to add people food to that, carrots, peas, broccoli, spinich. Food process. If you like to add supplements, then do this too, but don't make it too mushy.
It stinks, but is good eating for fish and inverts.