Spices.....

[Targan]

Some types of seaweed are edible and can be dried for longer and easier storage.

Sticking with the coastal theme one should always keep an eye out for drifting globs of whale snot. Ambergris is high value rare commodity.

I seem to recall some kind of SE Asian seafood stock which is made by putting tiny shrimps, krill and other marine crustacea in a sack and burying it on the beach for a worryingly unhygienic duration.