My do-all pack is a Golite Pinnacle (now the Jam 70L). Done everything from daypack (admittedly too much for that but it's light so big deal) to 7 days. It has a good compression system. Also easy to strap on snowshoes if you need them.

For you I would go with the 35L version. They are often out of them (such as now) as they just order batches it seems.