Everyone seems to think Shane did something horrible, but I think there's an argument to be made on both sides. If they had stayed together, it's likely they'd both have died, and consequently Carl would have as well. Why should they both die when Otis is more responsible for the situation? Honestly, I thought Otis would die, but because he would realize this likely endgame and stay to cover Shane. That said, Shane should have demanded that Otis give him the bag first. Then they could make a run for it and if Otis couldn't keep up it wouldn't cost anything. I wish we knew how far it was to the truck so that it would be clearer how likely or unlikely it is that they'd both make it before the walkers got them.