Some examples from games I've played:
A toothpick of lightning (like the javelin, but great for getting out that hard-to-reach gristle)
Another bowling ball (this one was enchanted to turn corners. Pity you couldn't AIM.)
A big-honkin' book, carried by a Kender priest of Gilean. (it had two uses in combat: either she'd swat you with the book (about 1d6 damage) or she'd open it and show you all the cool places she'd been and all the maps she'd made...putting you to sleep.)
And finally:
A mimic. We had tamed a mimic in a low-level dungeon (about 4th) way back in the days of 1e. It had been abused by the evil mage that was using it to hide his wand collection, and my druid/fighter made peace with it. The DM ruled that the mimic's natural movement prevented it from travelling with us, so the other fighter and I carried it between us as a chest. Whenever we came across anything that it could eat (kobolds, goblins, cave critters, whatever) we'd yell "Lunch!" and heave it at the walking snack-pack. IIRC, we hit about half the time...