All you have to cook things in? (3)
I believe the answer is:
pan
'cook things in?' is the definition.
'Pan' can be an answer for 'cook' (thesaurus). I'm not sure about the 'things in?' bit.
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for pan that I've seen before include "all in many words, initially" , "Prefix denoting all, continent or world" , "Roast" , "A vessel; chimp genus" , "Toilet bowl" .)