Originally Posted by
shipwreck
If you have to have that big of a pack then a trailer is a possible solution. But like nickthebeard, an ultralight bag works for me, I use a g4 style bag that actually is about that big but designed for twenty or so pounds max. It rolls to the size of a soda can when empty. I sewed mine myself, the instructions and pattern are free online and there is a yahoo group dedicated to making them.
Ditto the G4 which you can buy pre-made from Gossamer Gear. I just got one on sale for under $80. I used to use their G5 which only weighed 8 oz or so but they discontinued that one. The advantage of the frameless pack is it's easy to use it as a stuff sack for your sleeping bag, or just roll it up inside a pannier. If you get your load light enough, you can put everything in your pack and not bring panniers. I tried that once and didn't like it much, but some make it work. I will probably try it again some day.
I enjoy multi-day touring to trailheads and then going on multi-day hikes. The pack is also a decent carry-on if there's a plane trip in your itinerary.
Good luck figuring out a system that works for you.