I really tried hard to convert my car to natural gas. I talked to the gas company, made a few dozen calls, and searched for days on the internet. It is a really good way to run a car without many changes. My problem is the best I could do was get a mexican made conversion kit but no way to fill it at home. When I looked around everyone said the mexican kits are pretty solid but not epa approved, though it doesn't matter around here it might in your area. But I would have to drive 100 miles away to fill it. The home filling system was not for sale, only for lease using a professional installer. Somehow they didn't even think the gas company was able to install it for me and would not sell the setup to me. I thought about using a pump from a nitrous filling station but it seemed like it was going to be a huge amount of work to get the whole thing together.
I eventually gave up on the idea. That was a few years ago and things are probably different now. If you manage to get one set up save your contact information for the companies, I will be right behind you getting it done
It is not carbon neutral though.
Moonshine for me is a very good setup also. The weather really doesn't get that cold here and I have lots of people here locally that can help me build a still and a free supply of wood. But making moonshine takes time. It is not really hard to make and once you get the hang of it then making it won't take any thought. Just having to mess with it every few days to keep a good supply flowing might get old. I guess that really depends on how much you actually need though and how much room you can dedicate to a still and barrels. Last time I looked there was some sort of tax break for making moonshine but I have no idea if it is still available or how to get it. If you use a wood fire and scraps instead of food crops it would seem to be pretty carbon neutral.
I have no idea what it takes to use old cooking oil or any other diesel setup. I will find out this summer if I have time because I now have a Kubota diesel tractor that I need about 15 gallons a month at most to operate and it would be nice to use bio stuff in it.