Ok, not so much a tourist trap, but a money saver. If you're on holidays in Ireland and you're driving, then don't forget to fill up the car before you cross the border into the North! Most people living along the border do exactly the same thing. Oh, and cigarettes are quite a bit cheaper in the Republic as well! Try to go for petrol when most of the locals are at work, or the queues at the filling stations can be quiiiiiite long.