For several years we always have carried our marriage license with us. Not that we ever had a problem with having two names on the registrations (also the title in our jurisdiction) but while south of Sonoyta a decade ago, importing vehicles with three traveling couples, on friend, with adequet funds, but not enough in pesos, and faced with the Master Card reader on the blink, his wife stepped up to use her Visa Card, and they refused her, unless they could produce a marriage certifcate! Without it, they had to drive back to the border, over 50 Km.return. I had both cards and we were through. The two couples we were traveling with, were also sent back to the border then, as they had not gotten copies printed there, of course not knowing that the "outpost" had run out of ink for their printer. There had been no bank operating there then.