I've thought a lot about this, as I have only one pack that is big is enough for more than an overnighter, and there's things I like about it and things I don't. I'm not plonking down money on another one, though, until I've sussed out what I really want.
The current (and future) pack:
CURRENT: Lid pocket that is marginally useful. With two safety pins, I can convert it to a summit pack, but I've never actually used it that way, and I have more comfortable dedicated small bags for day hikes.
FUTURE: Would really prefer a rolltop for better weather resistance, with possible removeable straps or a flap to lash something on top. I think McHale makes a flap that doubles as a hydration sleeve, which intrigues me. I love bladders but taking them in and out of my pack to refill is always a bit of a pain.
CURRENT: Mesh side pockets with dual side compression straps. I like size and placement of these but the mesh needs to go.
FUTURE: Solid pockets would snag less and drain holes would take care of water. No change to the straps except maybe to add a third one depending on pack size.
CURRENT: Added my own hip pockets. They are removeable, but not easily.
FUTURE: Hip pockets built for the pack and easily removeable.
CURRENT: wierd, laterally overlapping front pockets with vertical zippers. HATE HATE HATE these.
FUTURE: A simple tall bellow pocket with a velcro top flap.
CURRENT: NO daisy chains or lash points. Why, why, why?
FUTURE: Plenty of well-thought out chains and lash loops.
The kicker is that this pack is very comfortable–I bought it off ebay and totally lucked out on the fit–and I'm reluctant to start accumulating packs based on their features that may not fit as well. I will probably continue using this one until I can afford a custom pack. Probably a McHale. The last time I looked at Dan's site, I saw a number of my sketches were features he already offered on his packs.