I would recommend rotating your food more often. I tend to pack stuff I'd eat anyway so as it gets older just replace it with new food and eat the old stuff for lunch one weekend. Otherwise, putting softer foods in Tupperware or packing canned foods sound like the most durable options. I carry my lunch in a larger tupperware container to keep it from getting crushed by my books, works like a charm and as long as things are packed well it doesn't add much in the way of bulk or weight. It doesn't have to be completely crush proof to protect your food, a Nalgene is probably over kill.