Media/IT related things: programming, web coding, graphic design, school newspaper, video editing, blogging
Discussion groups: economics soc, politics soc, medics soc, dental soc - these will help with ucas too
could you do stuff like cooking club if you have the facilities to make quick dishes? this will be very popular and equip people for uni
science clubs could work too if they're practical... eg doing dissections or building bridges or learning how to make chemical fireworks etc.