what i do is stock up on supplies needed from the fish store when ever possible such as krill and silverslides and other typs of fish foods my list is very long.half of my freezer is dedicated to fish food alone.
as far as normal grocery store product as foods yes ther a quite a few you can use.
raw squid ,scallops,crab legs,(frozen they are easy to crack and remove the raw meat)raw shrimp,oysters,muscles,frozen fish fellets.any type of ocean fish.avoid fresh water catch