Great thread. I joined this site specificly because of it. A little background: I own an auto repair shop, I'm an L1 ASE Master of 24 years. I'm also an avid hiker and a certified Wilderness First Responder.
OK, on to the LBV setup. The first thing to consider before buying a pack setup is to figure out exactly what you are going to carry before you buy. My 3 day pack for the AT weighs 17 pounds. My favorite small pack is an Ozark Trail pack I picked up at WalMart. It has no waist strap, I added a chest strap to it with a web and plastic quick release clip from a tent repair kit stitched to the shoulder straps with Spiderwire Kevlar fishing line. I have hundreds of miles in the mountains with this pack. A waist strap is not necessary for a light pack, especially if it is properly supported form the bottom. On the trail I carry a small fanny pack with my pistol and a spare mag in it. I typicly wear it around back, as it is not necessary to "quick draw" out on the trail. If you see or hear bear or wild boar signs out there you have plenty of time to spin that pack around and be ready. The fanny pack has a waist strap, and helps support the weight of the main pack. This setup works very well.
My LBV is the tactical type with the pockets on the front, but a straight up web type is every bit as effective, maybe even better. I carry a small medical bag with this one that has a waist strap and is clipped in to the bottom of the LBV, so it is a structural part of it. I also have a MOLLE camelback bag mounted on the LBV. The pack I carry for the rest of my gear is a medium ALICE without the frame on it. It does not have a waist strap, and doesn't need it. The bottom support is the medical bag that it sits on. And it doesn't need a chest strap because the LBV has it. I also eliminated the shoulder pad straps on the backpack because the LBV already has them. The pads from the ALICE pack feature quick disconnect clips for "drop and go" capability. Without the pads, what I have done is to invert the lower 1 inch web straps and loop them thru the lower adjuster straps, then feed them thru the straps and loops over the shoulders of the LBV. There. Now you are fully padded and the straps will not shift off the pads. Now, the inverted straps have loops on them at the top. Stick them thru the rectagular buckle clips that were attached to the shoulder pads (at the top of the pack). Hold them in place with clevis pins. You know, like the clip you use to secure the receiver hitch pin for your trailer, only smaller. I got them at the local hardware store for 23 cents each. You can tie them to the LBV with zip ties or fishing line so you don't loose them. The idea is you can reach up over your shoulders and pull these two pins, and the main pack falls off. I mean falls off. And boom, you are mobile. And you still have all the essential gear on your LBV, your water, and medical bag. A truly awesome, cheap, and very good fitting usable setup.