If you need to take your guitar out into the world that requires protection, as you discover here. Never leave the house without putting the guitar in some kind of protective case.
Protect your guitar on the road
Most people don't even think about the guitar's health as they toss their favorite acoustic into the station wagon and head for the beach. But they should. Using a bit of common sense can keep your guitar looking like a guitar instead of a surfboard.
If you're traveling in a car, keep the guitar in the passenger compartment where you can exercise control over the environment. A guitar in a trunk or untreated luggage compartment gets either too hot or too cold in comparison to what the humans are experiencing up front. (Guitars like to listen to the radio, too, as long as it's not playing disco.)
If you must put the guitar in with the spare tire, push it all the way forward so it can benefit from some "environmental osmosis" (meaning that it's not going to get quite as cold or hot next to the climate-controlled passenger cabin as it is at the rear of the car). This practice also helps if, heaven forbid, you're ever rear-ended. You can pay a couple of bucks to have Freddie's Fender Fix-it repair your car, but all the king's horses and all the king's men can't restore the splinters of your priceless acoustic should it absorb the brunt of a bumper-bashing Buick.
A hardshell case is a better form of protection for a guitar than either a nylon gig bag or a cardboard-like soft case. With a hardshell case, you can stack things on top, whereas other cases require the guitar to be at the top of the heap, which may or may not please an obsessive trunk-packer. (You know, like your old man used to pack before the big family vacation.)
Nylon gig bags are lightweight and offer almost no protection from a blow, but they do fend off dings. If you know the guitar is never going to leave your shoulder, you can use a gig bag. Gig bags also enable an electric guitar to fit in the overhead compartments of most aircraft. Savvy travelers know what kinds of crafts can accommodate a gig bag and stand in line early to secure a berth for their precious cargo.
Protect your guitar in your home
Whether you're going on a long vacation or doing three-to-five in the slammer, you may, at some point, need to store your guitar for a long period of time. Keep the guitar in its case and put the case in a closet or under a bed. Try to keep the guitar in a climate controlled environment rather than a damp basement or uninsulated attic.
If you store the guitar, you can lay it flat or on edge. The exact position makes no difference to the guitar. You don't need to loosen the strings significantly, but dropping them down a half step or so ensures against excess tension on the neck, should it swell or shrink slightly.