Combine: Sort of. If you click the magnifying glass on an item, it will display in the middle of the screen. If you pick the right item from the inventory while this is on the screen, you can do things with it. Some items.

(SPOILER)I just got the other key, thanks for the tip. I thought I was supposed to go *out* that door though, was a little disappointed. Though it means the game is not over!