Computer in flipping pocket, mate (6)
I believe the answer is:
laptop
'computer' is the definition.
(I know that laptop is a type of portable computer)
'flipping pocket mate' is the wordplay.
'flipping' says the letters should be written in reverse.
'pocket' becomes 'pot' (as in to pot or pocket a ball in snooker).
'mate' becomes 'pal' (both can mean a friend).
'pot'+'pal'='potpal'
'potpal' written backwards gives 'LAPTOP'.
'in' acts as a link.
(Other definitions for laptop that I've seen before include "Aid for businessman" , "PC" , "Some work on this" , "device?" , "Type of computer" .)