Travel agents and airlines sell travel medical insurance. Do try to select a policy that pays the medical bill rather than only reimburses after you pay.
An example is:
http://www.imglobal.com/insurance_plans.cfm?imgac=182857&frames=0&app_method=1&CFID=364420&CFTOKEN=7f2c9e61bb963956-DB43CC8D-2264-F52B-AA83D40865E0FBF6