As others have said above, it depends what you will be using it for.
as
>>915165 noted, an Alice pack will serve you well for every day use. I have a Medium, which holds about ~39 Liters, and can hold a sleeping bag, pad, water, jacket, and food. If you need a bigger pack, as one might use for "backpacking", consider an internal-frame pack from any major brand (Osprey, ULA, etc.)
now if you don't mind, I'm off to sleep in the fucking woods lol
