Popcorn from a cheap easy popcorn maker, little melted butter and a shake of sugar, salt, chilli powder, paprika or cinnamon.
Mini egg muffins, I make 24 at a time and freeze individually. They take 30 seconds in the microwave. Just make like a quiche, add ham, chicken, mushrooms whatever and cheese and make in muffin trays.
Cheesy scrambled eggs (sounds weird but it's what the 12yo likes to make!)
Quick cheese quesadillas.
Any and all biscuits they can get their hands on.
Babybels, fridgeraiders and pepperamis
Supernoodles, mugshots and cup soups (but only the ainsley Harriet ones cos they are lovely and thick)