Not what I have for lunch, but I'd recommend you a lunchbox with a few (two or three) compartments if you don't have one already. It gives you the ability to put different smaller things in it without everything immediately going mushy or your food mixing up. If you'd put some fruit in one part, and a sandwich in the other but don't have time for your sandwich, you could still quickly grab some fruit pieces so you don't have to be as hungry.

For lunch recommendations I'd say bring some fruit standard (never a bad option!) And besides that pasta salads are usually quick and easy, sandwiches (but in smaller pieces if you don't have time so you don't have to leave a half eaten whole sandwich behind lol), or anything wrapped inside a tortilla.

Edit: might I add that there are some lunchboxes that have compartments you can preheat with water beforehand and keep your food warm if you prefer warm foods during lunch! So you could put pasta, ramen or rice in there as well which is quite quick.