Of course you can use potions and food in battle! It will indeed cost action points, and you have to do it in your turn.
(Dragonlance is a D&D setting/universe, quite popular in the eighties. More popular than Forgotten Realms at one point. I like the Dragonlance books a lot, and there were a couple of cRPGs that used the setting that I liked a lot too, more specifically the SSI Gold Box cRPGs. Magic items were rare. But we're making a different game.)
