I just gotta toss a comment on the pile. No knife is a good weapon against a bear. Bears are bigger, stronger, and faster than you... and they come with 20 claws and some number of fangs. The best weapon against a bear if you must kill one is a stout rifle, followed by a 12 gauge with slugs, and distantly trailed by serious handguns (.44 magnum, .454 casul). Even if you manage to kill a bear with a knife, you're going to take damage in the process, and it will likely be your end.

Of course, simply being alert and seeing the bear before it sees you (bears are not, by nature, subtle creatures) will prevent a situation from developing. Snakes, now, they are sneaky bastards. I don't have any snake experience other than watching them zap into the grass with startling speed as you're about to step on them.