You will need to wear clothes suitable for sporting activity. A tracksuit in winter or shorts and t-shirt in summer along with running shoes is fine. Don't wear anything expensive! If you have them, bring as many of the following as you can:-
leather gloves (gardening ones are fine, welding ones are better)
beanie (we supply helmets, but they don't have padding)
shin pads
knee pads
elbow pads
The club has all of these items, which you can borrow whilst you're starting out.