In addition to the great ideas already posted i.e. medical bracelets etc..
Everyone should carry an Adventure Medical wound closure kit. It comes with an assortment of sutures, syringes and dressing all packed in a waterproof case. I would rather put my trust in a pre packaged suture kit than somethign from middle of nowhere Mexico.
IN addition I highly reccomend carrying a few single use OR Quick Clot vials. If you take a spill and are bleeding this will stop it immediatly.