The private pilot, who did not hold a multi-engine rating, took off to fly to another airport to purchase fuel. About 7 miles from the destination airport, the right engine stopped producing power. The pilot switched the fuel selector to crossfeed and was able to regain power on the right engine. According to the pilot, both engines subsequently lost power when the airplane was about 2 1/2 miles from the destination airport. The pilot feathered the propellers and made an off airport landing on a road. The airplane traveled into a ditch next to the road resulting in substantial damage to the left wing and aft fuselage. A postaccident examination revealed no visible fuel in the fuel tanks.