1) Between-meals eater 2) Cookie-jar raider 3) Eater 4) Fridge raider 5) Knish eater 6) Many a deli customer 7) Midnight raider 8) Munchie muncher 9) One always snacking 10) One snacking 11) Person enjoying a light snack 12) Raider of a kind 13) Snack eater 14) Snacker 1) Eater 2) Snacker 
Nosher is British slang for a lover of food and eating.
[n] - someone who eats lightly or eats snacks between meals
snacker noun someone who eats lightly or eats snacks between meals
a person who snacks, esp. one who does so often or continuously.