Horn of plenty. Weights a lot and provides less food than gods.
EDIT: 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.
As far as I know you can only polymorph to stop burning,but you will continue to burn once you return to your original form. Although, polymorphing will give you precious time to find some healing.
Did you know that whips can be made out of quicksilver?.. I sure didn't.
EDIT: Turns out that it is not very practical because wielding it requires 184 strength.
Sooo...
I killed everyone in New Attnam, but I can't find the Left Nut. I used a lot of explosives, so can it be destroyed?
Or I should just wait until every corpse will rot and then use a scroll of detect material?