Having opened a shop for food, kept at it! (5)
I believe the answer is:
stuck
'having opened a shop' is the definition.
I can't tell whether this defines the answer.
'food kept at it' is the wordplay.
I cannot quite see how this works, but
'food' could be 'tuck' (tuck can mean food) and 'tuck' is found within the answer.
A single letter 's' remains which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
'for' is the link.
Can you help me to learn more?
(Other definitions for stuck that I've seen before include "Jammed" , "Fixed" , "Trapped" , "Will's thrust" , "Unable to move" .)