Found: I either sell them for something more permanent or drink em like candy.
Bought: I use them when needed. I only buy specialized 1-shot items. If I'm a caster, I get a scrolls (1-2 each) of spells I don't want to bother memorizing. This applies to wands, potions, etc as well.
In general, I don't like 1shot items. They almost always feel like a waste of money.