I have a day pack I use while skiing. Not sure how you feel about mountain house but I can easily fit a week's worth in there. Bonus, the day pack straps easily to my rack pack.
edited: too many adverbs
I have a 20L and 13L Sea to Summit Lightweight Dry Sack.
I used the 20L to store my sleeping bag, sleeping, clothes and odds and ends. I used the 13L one for food. I got both of them on the trail and they both lasted well over 1500 miles. Anything inside the bags stayed dry. The 20L sack recently ripped at the seams on a backpacking trip and I emailed Sea to Summit with a picture and they replaced it for free.