L.M.
My daughter loves ramen noodles with cheese (I only use 1/2 the seasoning packet). We make it in the morning and put it in a themos. It stays hot until lunch time. Mac and cheese is also good in a thermos.
My oldest didn't like sandwiches at all. So instead I would cut up lunch meat or chicken breast into cubes and some cheese into cubes and send along with some crackers, basically the same thing in a different way.