Found some handy dandy stacking divided containers at my Albertsons. They are Rubbermaid Snacker Take-Alongs, sold in a package of five. The containers are square with a diagonal divider, and a lid that fits really well. When I pack a dip for veggies in the little section, it doesn't slosh over into the half sandwich on the other side. My walking buddy reports that juice from melons didn't leak over to her garden wrap. I stack two of the containers in my insulated lunch bag, but three would fit easily.
This product doesn't show up on the Rubbermaid website. I only found it on the Ace Hardware site. The product number is 7A16RDFCLR.
I've started buying Sara Lee turkey or ham for my lunches because it comes in a sturdy plastic container that keeps the meat fresher. The container is very reusable with or without its lid. I'm saving them for use in my art classes. Since I buy about one package per week, I'll have a class set soon. They would be just as useful for packing a sandwich or salad for lunch.
Shopping and packing a waste-free lunch doesn't take any more time than shopping, packing, and often microwaving a lunch of single-serving prepackaged disposable items. Over the course of a school year, a family would save at least $250 per child by packing waste-free lunches. That money can go into the college funds! http://www.wastefreelunches.org/ has lots of suggestions for making healthy lunches that are better for kids, wallets, and Mother Earth.