I definitely agree with dry shampoo, the amount of times our showers have run cold and no one's wanted to use them, or you wake up late, dry shampoo is great.
An NUS Extra card would be cool though you can't buy that before a certain point because they all run out in August. It's not essential but I've noticed that it gives me bigger discount than a regular student ID card.
A pair of rubber gloves. From cleaning the oven to cleaning up sick.