Re: filler screws/drain plug
First try a hand impact driver and a hammer. If that fails, due to the stripped screw head, use a small cold chistle and a hammer to turn the screw CCW. Let the chistle dig into the metal of the fill plug, and rap it firmly.
If that fails, it is time for the easy out, however, you will likely succeed with one of the other ways, IMHO.