Food left in cooler (4)
I believe the answer is:
flan
'food' is the definition.
(flan is a kind of food)
'left in cooler' is the wordplay.
'left' becomes 'l' (common abbreviation).
'in' means one lot of letters goes inside another.
'cooler' becomes 'fan' (I've seen this before**).
'l' placed into 'fan' is 'FLAN'.
(Other definitions for flan that I've seen before include "Sweet/savoury open tart" , "pudding!" , "Open-topped tart" , "Open pastry filled with savouries, fruit or custard" , "Open pastry dessert" .)