Bread? It's mine, thanks (5)
I believe the answer is:
pitta
'bread?' is the definition.
(I've seen this before)
'mine thanks' is the wordplay.
'mine' becomes 'pit' (down the pit).
'thanks' becomes 'ta' (UK informal version of 'thank you').
'pit'+'ta'='PITTA'
'it's' acts as a link.
(Other definitions for pitta that I've seen before include "Bread pocket" , "I might have a kebab in" , "Partially-leavened bread of the Near East" , "Type of flat bread that's split to hold a filling" , "Greek unleavened bread" .)