I was also wondering when and what they would prefer to buy.
Because I already had my hands full time-wise most of the AI is really dumb, they buy whatever they can (not a repeat of an item they have, they can afford it, not full on items) randomly after they respawn as they move out onto the field until they can't anymore. I'm thinking of expanding this with different roles for characters that prefer certain items and also adding magic, physical, healing aura, etc items to match.