cold-soaked oats (using yoghurt or fruit juice) with fresh or dried fruit and spices
bread and butter - with or without various sandwich fillings
salad - with or without tuna, cheese, seeds, basil leaves etc (and I suppose dressing if you like that kind of thing)
antipasti (olives, sundried tomatoes... erm.. et cetera)
dips; with lettuce, carrot, cucumber, Pringles or tortilla chips
pork pie - with salad and pickles oh and coleslaw
corned beef slices quite nicely if put in the fridge for a bit
summer pudding (needs a lot of advance warning)
fruit and yoghurt
I have never tried tinned boiled potatoes - anyone know? Otherwise if you're prepared to cook while it's slightly cooler you could have cold potato, or pasta, in your salad. Boiled eggs too (you can have them still slightly soft if you're careful when peeling). Sausages are delicious cold, chicken pieces edible.
cakes, sweets, biscuits, crisps, peanuts, ice creams, beer 