Freeze-dried foods from such brands as Mountain House and Backpacker's Pantry are staples for multi-day backpacking trips, and many preppers also store them for emergencies since they store for years and only need hot water to prepare. By utilizing dehydrated and freeze-dried foods from the grocery store you can make your own meals that are tasty and easy to prepare for a fraction of the cost of commercial backpacking food.
Trailcooking.com is the main resource for this method and features recipes, tips on dehydrating your own foods, and even plans to make an insulated cozy for freezer bags to reduce cook times. Most of the ingredients can be sourced at your local grocery store, but a few (such as single serving packs of olive oil) may have to be ordered online. Update - a helpful reader just informed me you can snag a few single-serve packets of olive oil at the Subway fast food chain.
Once you've assembled the ingredients for your recipe all you need do is put everything together in a freezer bag, label it, and when you're ready to eat you'll just need to add almost-boiling water, stir, and close the bag and wait typically 5-15 minutes for your meal to rehydrate and cook. You'll definitely want actual freezer bags as sandwich bags are not rated for high temperatures.
From my research it seems that Ziplock brand freezer bags do not contain BPA and are rated to be safely heated to microwave temperatures. As long as you're not immersing the bag in boiling water there should not be any health risk with regard to the bags. Freezer bag cooking seems to be a great compromise between tasty meals, ease of preparation, and cost.
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Thermos bottles were designed to keep hot beverages from cooling down so workers could have a hot cup of coffee all day long. Their insulating properties make Thermos bottles ideal to cook foods that take a long time to prepare such as oatmeal, dried beans, and whole grain cereals. Simply bring your ingredients to a boil and pour everything into the thermos and give it time to cook.