Except for clocks and fish skeletons?
I'd say backpacks full of gunpowder. They are generally unsafe to be around, so I rather let them rot on the floor and keep my distance.
badbeaver wrote
If you have teleportation control, scroll of teleportation can be a very useful tool for getting into secret rooms. Even though they are not optimal, they can be used for trivial tasks and save you teleportation wand charges.
That's exactly how I use them.
Also horns of plenty can generate carrots and other special food items, though with deliberately low chances.