During a cross-country flight, the engine sputtered twice and the pilot performed an uneventful precautionary landing, in a field about 20 miles away from his intended destination. The pilot then secured ground transportation and obtained more fuel for the airplane. During the subsequent takeoff from the "L-shaped" field, the airplane drifted right and struck a culvert on the right boundary of the field. The pilot continued the takeoff and landed at his intended destination. Examination of the airplane by a Federal Aviation Administration inspector revealed damage to the nosegear, lower fuselage, and firewall. The pilot also reported no preimpact mechanical malfunctions with the airplane.