If this question is being asked while visiting one of those inviting outdoors shops, the answer is frightening: everything! As it is always a good advice to never going shopping for groceries when you’re hungry, likewise you should never go shopping for outdoors amenities, unless the burning need and regret from not having handy a specific tool or support item has been already experienced in a real occasion. As a matter or facts, the zero budget approach is probably still the best. Shoes and foot comfort is probably number 1 in the list; second is likely some protection from the wheather, third the minimum gear for spending the night and getting the so deserved rest. The other real necessities such as a decent shower, drinking water and food will have to be sourced locally, and so be it.