It really is better to start out with the rest of the gear and then buy the pack. The space things like tents and sleeping bags take up can vary a lot. Also your size has a lot to do with the size pack you'll need and what will fit you. The climate and the time of year is a factor. Cold weather stuff is a lot bigger than warm weather stuff. Another point is that weight you'll be carrying will affect the type of pack you'll need. BTW Pack size rating is a bit nebulous. Some makers include pockets and extension collars some don't so take the size in the catalog as a starting point. For reference a 5 gallon bucket holds 1150 cubic inches. If you can't find what you want in a local store most good online dealers will let you return a pack you don't like. If they won't shop someplace else.