For getting gear (clothing) to fit better inside the pack, use a large Ziplock (gin, the freezer kind) and pack your clothes in it. 

then seal it *almost* all the way. Start to roll the bag TIGHTLY from the bottom, squeezing as much air as you can. The finally finish the seal. Voila, a vacuum seal bag for your clothes. 

I used to do this when I carried a much smaller pack for day hikes. I’d take a puffy or other airy layer and was able to save substantial space 

“Between every two pine trees there is a door leading to a new way of life.” (John Muir)

Superusers do not speak on behalf of REI and may have received
one or more gifts or other benefits from the co-op.