Dads are notoriously tough to shop for. But my dad is usually a breeze. Still, there’s one gift I’ve given him that stands above the rest: a subscription service that helped him write a book. At age 68, my dad has a slew of interests that have long made it easy for my brother and me to find gift-giving inspiration. He loves theater and live music, so we got him tickets to Merrily We Roll Along and Lake Street Dive. He’s an American-history buff, so we’ve given him biographies of John F.