I like a bunch of deli "Stuff" in the bento box things. Lots of small boxes with a fitted lid to keep everything separated during travel just as you packed it.
Hummus and carrots, pasta salad, fruit all chopped and ready to eat, crackers and dip, salads with dressing separate until time to eat. If you want something hot, get a really good thermos so nothing cools to much YUK. I have had to pack a lunch for 40 years and I don't often have sandwiches, but I still like a good PBJ. I like to make my sandwiches in tortilla wraps. They don't seem to be as messy when I get around to eating them....