Outside the U.S. I think I have at least three resources:
I bought an 'N' supplement to Part B. This provides some coverage for international travel.
For major trips, I buy emergency medical and evacuation packages. You can buy this annually as well. Usually, it is limited and secondary, and for major emergencies.
For the small stuff, up to a few thousand dollars, I'll pay it out of pocket. I probably wouldn't travel if I thought I could not afford to take care of medical care costs. You sort of need to be able to do this, because in most places the terms are "pay when services rendered" and you deal with insurers about reimbursement.
P.S. had my appendix taken out in Barbados, friend broke a leg in Rome, so have some experience with this.