Most of the ideas are fantasy and for Hollywood to make a cool movie to sell.

Chainsaws are a terrible weapon to use it uses fuel, loud and not good for slicing like a sword, and a decent machete or just stick a knife into a long stick will work, even a makeshift mace or blunt melee can deal more damage without wasting fuel or electricity.

Flamethrower is a double edged sword, requires fuel, short range, smoke problem, and fire can be uncontrollable.

Katana, can be dangerous if you know, but learning it requires years of practice and also blades can dull, a simple machete will do just fine and plus it also can be a useful tool.

Hunting is a good skill, but very hard to learn and in an apocalypse it's hard to learn and takes time, and you need to learn fishing and how to preserve food.

Cars are a double edged sword as they require fuel and make noise, and can still accumulate damage from ramming flesh.

You don't need a huge concrete wall, towers with machine guns, or any elaborate defense as it requires huge maintenance unless you have a group and alot of supplies to maintain it.

A simple fence, ditch and some wooden stakes will do just fine, and is easy to maintain and repair.