Very popular party with good snack food (3,3)
I believe the answer is:
hot dog
'snack food' is the definition.
(I know that hot dog is a type of snack food)
'very popular party with good' is the wordplay.
'very popular' becomes 'hot' (I've seen this before).
'party' becomes 'do' (do can informally mean a party).
'with' means one lot of letters go next to another.
'good' becomes 'g' (abbreviation).
'hot'+'do'+'g'='HOT-DOG'
(Other definitions for hot dog that I've seen before include "Sausage in a roll for feverish canine" , "Sausage in a bun" , "Sausage snack" , "Sausage sandwich - acrobatic skier" , "Sausage in bread roll for thermal canine" .)