Laptop boxes fit for purpose (3)
I believe the answer is:
apt
'fit for purpose' is the definition.
'apt' can be an answer for 'fit' (apt means appropriate or fitting). I am unsure of the 'for purpose' bit.
'laptop boxes' is the wordplay.
'boxes' indicates the answer is hidden within the clue (to box can mean to contain).
'APT' can be found hidden inside 'laptop'.
Can you help me to learn more?
(Other definitions for apt that I've seen before include "clever" , "may be appropriate" , "apartment in Queens, say" , "Suitable for Pat" , "Suitable; quick to learn" .)