If the world is going to "undo" everything I "do" in those 72 hours, I'm heading for the nearest armory and breaking out the medium machine guns and the antitank weapons. Then I'm going to steal an Abrams. (They have a few up the road, apparently.) I'd also like to build a really good HO-scale model railroad.
If the effects of whatever I do will still be around when everyone pops back into place, this would be a good time to stockpile cash, bearer bonds, gold bouillon... Having secured my future, and the future of my family, I'd go about building that model railroad.
Also, I'd like to take a spin in a really fast car.