Anything you can just rehydrate, really. When I’ve done MM’s, Polaris etc in the past we had 3 or 4 smaller ‘meals’ over the evening, so it was just a case of boiling water and not having to wash our pan out.
Basics like Smash, instant noodles, couscous and cuppa soups work well, especially if you’ve got a little bits of stuff to pep them up with – pepperami, Babybel or mini prepack cheeses, small tins of sardines etc have all made appearances in the past, as well as carrying the standard service-station sachets of salt, pepper, ketchup. If you’ve pack space, take one of the smaller Pot Noodle-type things and use the pot as your bowl for all courses, then bin afterwards. Instant just-add-water custard gives you a bit of dessert, if you carry dried fruit for the day you can lob that in it as well. I’ve seen people use things like MountainHouse dehydrated meals but they seem like a lot of cash for no extra benefit.
A favourite trick in the past as well, since a lot of people end up with salt cravings at the overnight, is to prep a packet of crisps beforehand and have them in a pocket for camp. Pin-prick a corner of the pack, gently squeeze the air out (and crush the crisps a bit), then tape over the pinhole. That one’s made a lot of people jealous/salivate at overnight camps over the years.