Que Sera- Oddmanout has it down and it looks like you agree. The rental suggestion is a good one too. I've helped set a lot of folks up over the years, the pack should actually be your last piece of gear. You need to nail down what fits in the container, before you buy it. Frameless packs from the cottage guys are awesome, but you need to carry under 30 pounds- or they suck. You won't find items like that at REI. Your sleeping pad and sleeping bag choices could easily fill up 20L of pack space alone. Seasonal conditions are a huge deal too. I usually let folks borrow my packs to get started- I suggest you "borrow" from your buddy's at REI until you nail down more details. If you have access to backpacking light, check out where they are heading. They are pretty much arriving at the same conclusion that Oddman has- you can have one basic kit that you can tune a bit, and a slightly bigger pack than your typical SUL pack makes sense for that reason. I plan my packs on a worst case of 7 days food by taking advantage of simple expansion collars, but if you are AT specific- 5 days or less is fine. I use a Neo-air and a summer quilt to keep pack volume down- I have a roughly 30L pack with everything blown out that holds seven days food- but that took a lot of tinkering. As Oddman implied; on a weekend trip, you have less food- so you can haul a few creature comforts in the extra space. (A good plan too to keep you in shape!) A basic pack like a GoLite Jam for $100 bucks in 36L size can do the job without breaking the bank. I have started a lot of folks off on that pack, depending on rental rates it may be cheaper to buy that pack to start out. Two or three weekends of rental fees may cover the cost. It sounds like even if you won't be a gram weenie- you still want to keep things tight- as others mentioned, a smaller pack forces you to think. If you are a member check out this article- http://www.backpackinglight.com/cgi-...et_part_2.html If not a member- it's only $25 a year, and well worth it to help you along as long as you don't get too turned off by the engineers over there.