An attendee sits among snack food on a picnic blanket during the 2016 Chap Olympiad, at Bedford Square, in London, U.K. (Photographer: Charlie Kwai)

The Perfect Picnic Drink Is a Refreshing Tequila-Watermelon Cooler

(Bloomberg) -- Picnics call for refreshing, unfussy long drinks—Arnold Palmers, mojitos—drinks that don’t take too much prep and provide ample hydration. But moreover, ones that hold up well to tra...