The best way to ensure coals are fully extinguished is to dump a bucket of water on them and stir them around. Feel around in the sludge to make sure all the coals are cold. Make sure you get all of it out of the grill because it will damage the bottom. In bear country, treat the ash, sludge, and anything used to clean the grill the same way as food and scraps. Otherwise, bag the waste and pack it out or, if conditions and regulations allow, bury it away from the campsite.