It isn't something most people like to think about, but injury or illness while travelling is always a possibility. Buying traditional out-of-country medical insurance is one way to deal with the unexpected expense, but insurance can be very expensive or even unobtainable for people with certain medical conditions.
In cases like that, a company called http://www.MedjetAssist.com could be a good alternative. If you are admitted to hospital more than 150 miles from home, it will provide transportation by air ambulance to a hospital of your choice near home. So long as you are under 75, no medical questionnaire is required, and rates are reasonable. For individuals, a year's membership costs $255 U.S., while a family membership is $385. Corporate, expat and senior rates are also available.
This type of program isn't as comprehensive as good travel insurance. It doesn't cover any relatively minor ailments or injuries, or cases where treatment in an emergency room is all that is required. Nor would it (or any other medical insurance) be of much use in very remote areas far from any hospital.
The days when you could stay overnight in hospital in Spain and leave with a bill for $50, as I did once, are gone. Particularly for travel to the United States, travel health insurance of some kind is a necessity. MedjetAssist is available to residents of the U.S., Canada and Mexico or expatriates from those countries.