Aspirin works pretty well to revive a battery. Crush it and put it in the cells. About 1 per, IIRC. Learned that from my Dad on the farm.
They used to make an additive that prevented batteries from sulfating, but I can't find it anymore. Farm supply store, maybe.
Coke will eat the crud right off a battery terminal. So will baking soda and water. DO NOT get that in the battery. Rinse well. Also good for cleaning the frame around the battery. Neutralizes any battery residue.
Now for the McGuyver tip: Carry several pieces of steel coat hanger. The old, heavy duty kind. You'll know when you need it.
I've been shot, cut, burned, blown up, fired, busted, promoted, reprimanded and decorated. What are you going to do? Ban me?
Blessed be the Lord my God, who prepares my hands for war and my fingers for battle. Psalm 144:1