Don't.
In a SHTF environment, do you want to make it use MORE gas?
Look, the LAST thing you want in a post SHTF world is a shoot-out.
The best way to avoid that, is to just stay away from everyone.
If you see someone post SHTF....HIDE. At least until things settle down.
You may be like a Walking Dead fan, etc. So you're used to seeing these shootouts.
OK, now think about Hershel's farm. Know why he survived so well, as an older guy, and with two gals to look out for? Because he was HIDDEN all that time....that's why.