[ 100% Correct Assumption Award, except Ferrus is partially worse off then he is because he makes friends but Jamie is sort of aware that when he started writing Ferrus Ferrus sort of had (and still has) issues with thinking people are his friends but not knowing what do with a friend... ]

Probably constructs, mostly, and probably a variety of potions. When I had Ferrus, I made a lot of various potions, though I gave half of Ferrus's stash to a friend when I found out they were stuck in Zender.

I sort of memorized most of the useful potion combos, since it made it easier to have reasons for Ferrus to be out and about. Having him gathering materials, and stuff.