Lift Bag
Lift bags are commonly used for recovering heavy objects from the bottom. The bag is simply tied on, inflated from a regulator, and shot to the surface. An often-overlooked use for a lift bag is to get yourself to the surface in a safe manner when you have become lost and can't find the anchor, or if the anchor has pulled out of the wreck. Using your reel as described above, you can shoot a bag directly to the surface and then ascend on the line.
However, under such circumstances, I prefer to get myself off the bottom and up to my decompression or safety stop depth as quickly as possible, and then deploy a bag to the surface using a short length of line attached to the bag for just that purpose. Either way, the bag marks your position for the crew of the dive boat. You should write your name in bold letters on your bag, so you can be identified before you surface. The bag will also keep you from being sucked down to the bottom if there is a strong current. Most lift bags have open bottoms. A bag like this can hit the surface, tip over, and deflate. For self-rescue, as described, you should use a bag with a self-closing bottom.
If worst comes to worst, and you must do a completely free ascent and drifting decompression, sending the bag up will at least allow the boat to track your position. A 50-pound bag is adequate for this purpose and will fold up quite small and stow away unobtrusively until you need it. Orange or yellow are the best colors for visibility; a white bag can be very difficult to see in a foaming rough sea. The miniature "safety sausages" that are available are simply too small to be of any use around here.
The OMS 50 pound Surface Marker Buoy ( SMB, right ) or something equivalent should be part of every diver's equipment. This buoy has a one-way inflation valve to prevent it from "blowing over" at the surface. This bag is designed for emergency use, although in a pinch it functions perfectly as a 50-pound lift bag.
DIR
DIR-F recommendations for surface marker buoys and lift bags are quite reasonable; ie, the same as here.