Yes, usually easy to carry enough food for the day. Sandwiches, or homemade carrot cake, or flapjack, or malt loaf (Soreen is not vegan, but most supermarket brands are).
For buying in shops:
Crisps
Peanuts
Bananas
Chocolate - Bournville is fairly common, and a few shops have Green & Blacks, or Lindt or Ritter Sport etc
Pitta bread or oatcakes, with hummus or peanut butter to spread on
Cereal bars / flapjack - there are a few vegan brands
Irn Bru
Pot noodles, if the garage has a kettle
Skittles, Starbursts