Asda self-checkout machines: any change in notes is dispensed at the bottom, the number of people who walk off without taking their £5 change is scary. A few times now I've taken someone else's fiver because they'd walked off and were nowhere in sight to give it back to them.
TV licences: if you get one then hold off getting one until a month or so into term, then pay on quarterly payments - on monthly payments by DD you pay for the entire year within the first 6 months, on quarterly you just pay for each quarter as you go, so when you move back home in the summer you can cancel the DD and you've only paid for 3/4 of the annual fee.