Get Every Last Drop At The Pump
When you fill up on the station forecourt the pumps work out how much to charge by how hard you are holding the nozzle-operating lever and for how long. When you take your hand off the lever the petrol doesn't just stop coming out instantly, there is still quite a small flow of petrol. When you take your hand off the lever (because you are about to reach the amount you want to spend) make sure you give the pump quite a few seconds to let all the petrol flow out, you can even give it a shake to get every last drop.
Not only will this ensure that you get all that you pay for but it will also stop splashes when you go to put the nozzle back on the pump so it won't hit your paintwork or go on your clothes.
There isn't any! If you are so busy you don't have 2 seconds time to give it one last wiggle to get every little sprinkle you can then there must be something going on that you need those 2 seconds. As a popular supermarket chain would say "Every little helps" and in this case you might as well embrace that.
Image credit: sxc / egilshay 2008.