For inclusion in a kit I really don't find much use for a single-purpose gas-shutoff tool. Generally a largish Crescent wrench (8" or better), monkey wrench (recently found out you can still buy those), a pair of Channellocks (8-12"), even a large pair of pliers, like Vise-Grips (8" is as small as I would consider) will often work if the valve isn't bound up.

The advantage of any of those is they are general use tools that can earn their keep, and the effort use to schlep them around, by doing many other jobs. Crescents wrenches are good on a wide variety of nuts and bolts. Large Channellocks do plumbing, grip a huge variety of objects very well, and pull nails. A pair of Vice-Grips is a clamp, hand vise, pipe wrench, wire cutter, etcetera.

If you are setting up a tool to be kept at or very near the gas valve, preferably chained to it, a purpose made tool makes a lot of sense. I've seen pieces of metal bar stock with a rectangular hole cut in one end that are good. Simple enough to make if your handy. The advantage there is that, unlike a Crescent wrench, which might be used anywhere, the bar stock with a rectangular hole is pretty much a one-trick pony. It is made to fit that valve and little else. It is not likely to be lifted by your no-count brother to work on his jalopy. Chaining it to the valve also helps eliminate wandering.

Most of the tools sold as "gas-cutoff" tools are catering to the disaster preparedness crowd are, IMHO, too specialized to earn their keep in a survival kit but, paradoxically, to multi-purpose to chain to, or hang by, the gas valve and expect to stay there. Most are also overpriced.