I'm looking for a backpack system that will combine a few worlds: day hiking, camping, backpacking, and go-bag. I envision that the day hiking contains the essential things (water, snacks, change of underwear, towel, etc.) and can be used for day hiking and a go-bag. If I'm going with a meal, I attach another bag (preferably by clips) with the food stuffs. If I'm going to be staying overnight, I can clip on the bag that has the sleeping equipment.

Has anyone seen a good arrangement for this?

I'm focused on simplicity, though if the price is too high, packing doubles of everything might be better. I consider that an annoyance, but that's a lot better than repacking bags for every trip and forgetting things.