Plainclothes pigs will often have protective shoes with reinforced toes.
Bring foam earplugs, dust masks, and bandanas to demonstrations/when doing direct action
Mask up, but wait to mask up; you'll want to cover your face if things get out of hand, but if you arrive wearing a mask, pigs may sniff you out.
The more medics, the better. Carry a first aid kit on you.
Bring literature! If you can't participate in direct action, supplying people with zines and other literature will help the left grow.
Remember: the police are the fascist footsoldiers of the elite. Never trust them, never tell them anything.
You can stitch with dental floss instead of thread. Cheaper, more accessible, generally sturdier. You can reuse the box for storing small items.
Try to buy jackets secondhand.
Be careful not to wear your scariest studs/spikes into the pit, or you might take someone's eye out. Bullet and short pyramid shapes are generally safest.
Pin backings are a good investment if you want to keep your pins. Insert the pin through any rubbery, thick material you can find (eraser, piece of a toy, etc) before securing it. If you have the equipment, you can also solder pins shut.