short answer, although it would mean more code than Nick's version:
look for the put() command
look for the has() command
look for the obj.in.room() command
if your character will be dropping their inventory items in a particular room, you can use put() to put the inventory items in the room (after you test if the character has the item by using has()). Then when your character comes back to the room later, you can test obj.in.room() to find out if the object is in the room (which it will only be if your character had the item in the first place).
Nick's method would mean less code and it automatically works for all inventory objects that the character has, so I personally would recommend using that, but I'm just throwing out the simplest to understand (not the optimal) way of doing it.