I fill every 1/2 tank or MORE often - but I don't drive that much - the truck has a 20 gal tank, and gets 12 mpg city - so every 120 miles....

My OLD truck (which in many many ways I wish I still had) got 22 mpg city, and had a 30 gal extended range tank - I LOVED that - 300+ miles between fillups - aka I'd actually fill < 1/month (told you I don't drive much)

That said - I got the truck for reasons OTHER than bug out - but there are 4 large boxes of bug out/emergency gear stowed in the truck