I have a Zero, size small and the only options is a front mesh pocket and some loops so that I can strap a GG SitLight pad to the outside as the frame (when I choose to carry it) My regular size, Original NeoAir is always my frame in this pack.
I have carried up to almost 20 lbs in this pack and it has been great! I mod'ed it to add my own hip belt (which is also the hip belt that goes with the Multipack) however, I have hardly needed it.
For me, here in the Southeast and with our temps, this is really a perfect 3 season pack for me. I can easily fit some extra clothing and 5 days worth of food in the pack and still have a little extra room. In the hottest part of the summer, it is almost too big…I try to let my quilt loft up to take up the room, but the weight of my food will make short work of that… it is still great though…
For (our) true winters I have a Blast 30 pack, which is a little bigger than my Zero, and also has a real hipbelt. This pack is great for those hikes, however, I will be checking out a GG Gorilla pack this winter… No real reason to change out my packs, other than just wanting to try the Gorilla due to curiosity…
Anyway, if you are interested in how much stuff fits in the packs (Zero & Blast 30) here is a review I have on them, along with some video of everything in the pack…
Zero Pack review with video:
http://sticksblog.com/gear/my-current-gear/backpack/zpacks-zero-backpack/
Blast 30 Review with Video:
http://sticksblog.com/gear/my-current-gear/backpack/zpacks-blast-30-backpack-multipack/
Here is another video in which you can check out what I put in the Zero, and is a bit more than what is in the first link. Check out the video about 15:30 in for an unpacking:
http://sticksblog.com/gear/my-current-gear/backpack/zpacks-blast-30-backpack-multipack/