Great Isotonic Sports drink at only 50p a bottle, available in Cherry & Tropical Fruits flavours (Red & Blue) online and in store. Stop paying £1 a time from the vending machine and plan ahead, I've just bought 8 packs in the last couple of weeks.
Both flavours are just £2 in store for 4 bottles, although online it seems only the Cherry is £2, the Blue is £2.28, which is still a fair price. In store would probably be the best way of getting these as you'd have to spend a certain amount online to get your free delivery; fine if you shop online at Asda.
Not the cheapest ever deal for Powerade, but it's the best price I've seen at the moment, the drink definitely makes a difference when playing sport.