Bill goes in to snack (4)
I believe the answer is:
taco
'snack' is the definition.
(I've seen this before)
'bill goes in to' is the wordplay.
'bill' becomes 'ac' (short for account).
'goes in' indicates putting letters inside.
'ac' placed into 'to' is 'TACO'.
(Other definitions for taco that I've seen before include "Filled rolled tortilla" , "Mexican dish of rolled tortilla with filling" , "Tortilla rolled round a filling" , "Folded and filled tortilla" , "Set of three" .)