With regard to shovels, the plastic ones are very inadequate for serious digging in frozen or compacted snow, The steel ones such as the Voile are much better. (I carry a Voile on my winter pack for avalanche rescue.) Keep in mind, however, that one can get stuck in lots of situations other than snow. I once had occaison to dig out hard packed, well consolidated dirt, with some gravel mixed in. In this situation, even the Voile might not be optimal.

For carrying in a vehicle, where weight isn't such a huge consideration, a really stout shovel isn't a bad idea. In one car we've carried an old style, genuine GI entrenching tool, which fits in the space around the spare tire. In the other car, we've carried the "NATO" style e-tool, which fits in the smaller space available in that car. Make sure you get the genuine issue shovel, as there are some cheap knock offs, which will break or bend when you need them most.