The best thing you as a hermit can provide is usually big hunt (bears), and foragables (flotsam, pearls, bluebells, edelweiß). You are essentially trading the time it takes to do a simple task (hunt/forage) they could do themselves (a service), for something they have but you need (a product).
That's probably your best route to go, if not, take a look at some of the trade threads and see what they're after.