Old jeans, top or hoody, some sturdy boots (preferably with ankle support) gloves & scarf to protect hands and neck & maybe a hat (takes away a bit of the sting)
Yeah - any dark clothes you don't mind getting dirty! Plus some boots.
If you've got nothing suitable, then a quick trip to your local market will probably get you some dirt cheap army surplus trousers and a jacket. You can always use them as "decorating" clothes after