Millions has been raised by fast food restaurants like McDonalds with a simple way of leaving the change (or some of the change) from your meal. This works because we are given our change whilst we wait for our food.
Increasingly I find myself self serving in shops.
When you pay with cash the change lands at the bottom. The brilliant idea is to offer a question on the screen asking whether you want to donate to a range of charities.
I think most people would donate. I would. This could be thousands of small donations every hour!