Relative picked up hot snack (4)
I believe the answer is:
nosh
'snack' is the definition.
(nosh can mean food)
'relative picked up hot' is the wordplay.
'relative' becomes 'son' (son is a kind of relative).
'picked up' says the letters should be written in reverse.
'hot' becomes 'h' (abbreviation eg on taps).
'son' written backwards gives 'nos'.
'nos'+'h'='NOSH'
(Other definitions for nosh that I've seen before include "Slangy food or meal" , "Food (Yiddish)" , "Eat (sl.)" , "Scoff" , "A slang meal" .)