When you need to quickly haul a pack or small haulbag, instead of doing the forearm-flaming hand-over-hand haul, tie a Garda hitch in the haul line. The Garda hitch is a one-directional, self-locking hitch that lets you haul, but lets you relax your grip when you tire. Using it prevents your accidentally dropping the pack.
Ideally, use identical oval or "D" carabiners, which allows the smoothest operation. Avoid locking carabiners, as they can prevent the rope from locking down properly.
To haul the pack, simultaneously pull up on the load side of the haul rope and down on the brake side of the rope. Do not just pull on the brake side, because the garda hitch adds a LOT of friction. An informal test I did with a spring scale and a 10 pound barbell weight showed it took about 60 pounds of pulling force to lift a 10 pound weight through a garda hitch; just 17% efficient. That is terrible! So, be sure you lift UP on the load side, and not just pull DOWN on the brake side.
Locking the knot is simple: just let go.
A few cautions - while some sources suggest this can be used in a crevasse rescue operation, many folks think this is not such a great idea because the hitch can be a little squirrely if the carabiners are not properly oriented, it's hard to release under load, and it adds a lot of friction to your hauling system. It's probably best to use this for non-critical situations such as hauling up a backpack.
Start with two identical carabiners clipped to the anchor, gates facing down and out. Clip the rope through both carabiners. The loaded strand of the rope is on the left.
On the right side of the carabiners, make a small "silver dollar" loop with the rope.
Clip this loop into the right side carabiner.
Done. The loaded strand is on the left side. If you pull on the right the load will come up. If you stop pulling, the load tensions the carabiners together, pinching the rope.