This story, from then-White House Special Assistant Joseph A. Califano, Jr.
"In the early afternoon, the President, with me next to him in the front seat, took his white Lincoln convertible, top down, for a drive around the ranch. It was incredibly hot; the dust clouds made it hard to breathe. But there was relief.
"As we drove around we were followed by a car and a station wagon with Secret Service agents. The President drank Cutty Sark scotch and soda out of a large white plastic foam cup. Periodically, Johnson would slow down and hold his left arm outside the car, shaking the cup and ice.
"A Secret Service agent would run up to the car, take the cup and go back to the station wagon. There another agent would refill it with ice, scotch, and soda as the first agent trotted behind the wagon. Then the first agent would run the refilled cup up to LBJ’s outstretched and waiting hand, as the President’s car moved slowly along."