Pick a cause (say, VillageReach). In two similar locations, run a donation drive for it; in the first, have a bake sale (or other quickly consumed goods), in the second, sell those little cause-promoting bracelets (or other lasting tokens). Test altruism in both an hour later (purchase of moral satisfaction) and a week later (foot-in-the-door).

Also, a study on smokers showed that asking people to stop smoking for a short time makes them more likely to accept stopping smoking for several weeks, so tokens seem unecessary for foot-in-the-door.