Hmm...a bit limited in your options.  There's always wraps and hummus, which are my fall back when I don't want to cook.  A salad, prepared shortly before you go to class, should still be crisp when you eat it.  A meal bar and a veg or fruit would be a decent last resort.  Also, buy one of those insulated lunch boxes-they will keep cold stuff cold and warm stuff warm.

I agree with the lunch box idea. You can freeze an ice pack or two and get and insulated lunch box-then you could pack whatever you wanted. I do it all the time for lunch at school

Cook something the night before that can be eaten hot or cold.

Tonight i had chickpeas with some stir fried veg and a jacket potato. For lunch tomorow i will have the same but with cold brown rice. I like to mix a little bit of tomato sauce or a sppon of tinned tomatoes to stop it going dry

I cant decide wether i prefer it hot or cold!

My boyfriend makes a tex-mex marinated salad with tomatoes, corn, black beans, and edamame marinated in vinegar, sugar, lots of cumin and chili powder and garlic.  It's quite good, high in protein with decent fiber, and holds pretty well, especially in a cooler lunchbox. 

And the old classic pbj is vegetarian and holds just fine, too!  Pack some carrot and celery sticks and an apple and you've got a great meal.

Stuff a pita with some hummus and veggies and put it in a zip-lock and keep it in your purse/bag/whatever.  It will be fine for a few hours.  I have done this many times going to work.  PB&J are always yummy too!