I have dispatched several deer with a knife to the throat and I almost always have a very sharp knife handy.... a few were while hunting, but I have dragged two out of the road that were injured enough that they couldn't stand or wouldn't survive for sure. Both got dragged off the road beside(out of sight) the truck and dispatched. Hold them down, especially a racked buck's head until they expire. It is quick and pretty humane imo and all you need is a sharp knife, just slit the throat through the windpipe towards the spine and they will expire quickly.