Seaweed isn't magical. By that, I mean seaweed isn't (Magical). The term "seaweed" is often used to describe any edible food that gives waterbreathing, and it's perfectly acceptable for ragers.

Seaweed = waterbreathing = not necessarily magic, is one of those things you just have to accept and move on with in CF.

As far as other stuff goes: Ragers can't wear (Magical) stuff. AFAIK, folks have gotten away with using just about anything that progs (does something in combat), as long as it isn't overtly magical. There are a couple swords, for example, that "do stuff" in combat but aren't flagged as magical.