So do you just buy a half gallon at a time, or do you pour out the excess? where? There are weeks when my car doesn't use over a gallon or two of gas, so what should I do with all that is left over that week because I was stupid and bought a tankful?
As far as additives being detrimental, I'd have to guess that must depend on the exact additive in question, because all pump gas gets a dose of additives before it comes out of the hose.