20 Down provides the clue to the puzzle’s theme: Cylindrical cardboard containers apropos for this puzzle? Answer: Bandboxes
The band is ELO, which regularly shows up in NY Times puzzles. Here, the three letters appear each time within one square or box. When the puzzle is completed, those boxes form a big box.
14A. Fruit salad item = Melon Ball
15A. Rich, cheddary party food = Cheese Log
37A. N.L. home run king until Willie Mays surpassed him in 1966 = Mel Ott
39A. Certain wildcat = Ocelot
62A. Moves = Relocates
63A. Camp employee = Counselor
Despite all the times I’ve filled in ELO correctly, I’ve never known anything about this band. So, I finally decided to investigate. First, to Wiki where I discovered that the letters stand for Electric Light Orchestra, and that it’s a British rock group popular in the 70’s and 80’s. Well, you probably knew that, but it was not an era whose rock music appealed to me. Then over to YouTube to hear their sound. Turns out, it’s not so unappealing.