SW quiche (search for recipe!). It holds together well because the egg makes it set. If you cut a piece off from a large quiche, or make mini ones, they will keep together well in a lunch box! When I was at uni I always had quiche, it was lugged about in my huge bag all day but looked fine when it came to eating it. No need for jacket potato!
Cooked pasta, you can have extra light mayo (check syns) and tuna, or mix some pasata with herbs/peppers/onion/garlic etc. Chill overnight and you have a yummy cold tomato pasta dish.
You can have sandwiches - have the bread (wholemeal) as a HEb and go for free fillings.
Cous cous is also a good choice - you get plain cous cous and flavour it up how you like or buy the cous cous packets, like Ainsley Harriot ones, but these do usually have a couple of syns so best check first.