Golden tablets with the seal of the ruler that issued the pass and the seal and name of who it was issued to. About the size of your palm of solid intricately etched gold. The holder of the tablet is backed by the authority of the king to make any required purchases on credit or enter any place they deem necessary. A very powerful token indeed.
Want to avoid fighter types focusing on swords? Make Longswords and Bastardswords the weapon of the Noble class, with a death penalty for other to carry. These weapons will be ornate and finally crafted. Adventurers will be stuck with cheaply made broad and shortswords, while professional fighters might use two handed swords.