You have subscriptions for lots of things: music, TV, maybe even magazines. So why not your car? Book By Cadillac is a new service that gives you access to top-tier vehicles for a flat monthly fee. Using an app, you select which model you want to drive — Platinum-trim Cadillacs like the XT5, CT6, Escalade and V Series are available — and it will be delivered via white-glove concierge. When you're ready to switch, they'll bring your new ride and pick the old one up. That means you can get a sporty CTS-V for a trip to the shoreline, then ditch it for an Escalade when it's time for your ski trip. And since you don't have to worry about things like maintenance, insurance, or a long-term agreement, you can simply sit back and enjoy the drive.