They'll last up to a week in a bucket of salt water, if kept cool. Razor clams are not the usual target of shellfishers. The name comes from both the straight-razor shape and shell's edge. You may catch one or two of these while digging steamers, if your trench is deep, but the best method I've found is stealth. Spot their oval siphon hole and approach with soft steps.
Razors have a very short siphon, meaning they are resting right at the surface.
But their foot is long, about 6 inches, and very fast. Make a flat plane with your fingers together. Point your fingertips at a 45-degree angle, down toward the siphon hole, but back from it an inch or more. The task here is to push your fingers through the sand and into the side of the razor, thus pinning it. Once held in place, use the other hand to dig it out.