ETSU makes a great point about the biggest volume killer being the sleeping bag. Many people push the bag into the bottom of the pack without putting it in the stuff sack. For some reason, it seems to take less room this way. It does leave it susceptible to getting wet if you don't use a pack cover in the rain.

One of my packs is a Talon 44. I just packed it with my cheap Alpine 20 sleeping bag and everything else. Basically, the pocket on the top flap is what is left for food. That would work fine for 3 to 5 days if I chose my food carefully. Keep in mind I've been through the process of learning what not to take.

However, it's a tight fit. I'd rather either have a good down bag that takes up less space or a 48 to 50 liter pack. In the Osprey packs the weight penalty is very small.

One thing to consider is buying a tent that uses trekking poles for support. That will save a little weight and volume.