Cheap and easy wheel chocks
Here's an easy method to make up some sets of wheel chocks to use on extrications or vehicle fires. They're cheap enough that if they get lost or burned up it's no big deal. You can get 8 sets of chocks out of an 8' treated 6X6, and you can spend as little as $15-25 depending on material costs.
There's a few good examples of cars on fire rolling away from firefighters on YouTube to justify carrying these on apparatus, not to mention that any car that you are performing patient care in should be chocked, as we have no idea of what condition the brakes and drive train are in.
I start by cutting the 6X6 in half, this makes it easier to handle. A 12" miter saw works best for this, but use what you have. Since I'm a woodworker, I like to pretty things up a bit so I'll run the two halves through a jointer to clean up the sides a little, but you don't have to. It just helps to reduce splinters and for better paint adhesion if you choose to paint them.
I then set up my 10" table saw with the fence 1" from the blade and the blade tilted at 45 degrees AWAY from the fence. Have the blade up as high as it will go. It won't cut all the way through so flip the wood and cut the other side so you are cutting off one corner of the 6X6 lenght wise. My saw still will not cut the corner off all the way, there will still be a narrow strip holding the corner on, so I use a sawzall or hand saw to finish the cut. You can use a jointer or belt sander to smooth this side. I then cut the two halfs to about 5 3/4" lenths (you lose a little to the width of the saw blade every time you cut so you won't have 6" pieces). I like to round off all the edges by sanding to reduce splintering.
You can use whatever rope you like, but I like using yellow polypropolene because it resists water, oil and rot, and it stands out. Drill a hole about 2-3" into one of the ends of each block slightly bigger than the rope you are using. I cut pieces of rope about 3' each to connect two chocks together. Use polyurethane glue to glue the rope in the hole, I put a little in the hole and a little on the end of the rope. Don't use a whole lot because the glue will "foam" and expand a bit.
I also like to paint my chocks to make them stand out a bit. I put on a good primer, and then yellow paint with sand in it for friction. You don't have to paint them, it just helps to remind guys that they're in the truck (so use them) and to pull them when you're done on the scene. If they get lost or burnt up, you don't have a lot of money invested, but they are a great safety item and well worth the effort of making.
(I'll post a pic of the finished chocks, don't have one here)