Portable Vs in-car systems
Some luxury cars come with the option of a built-in DVD-based entertainment system. If your car costs enough it may even come as standard equipment! These integrated systems can provide a much neater-looking system, with better sound and the convenience of overhead or custom headrest screens. They can even offer a screen in the front as well, which automatically switches off when the vehicle is moving (a legally-required safety feature).
The downside though, is these systems are relatively expensive (just ask your car dealer for the optional cost, but be sitting down at the time). The most obvious drawback is that they are limited to the one vehicle and can be targets for theft and damage.
A portable DVD player, on the other hand, costs (a lot) less; can be used in multiple vehicles, then taken out of the car into the home, hotel, tent, bus, train, boat or waiting room and used with or without a big-screen TV. And, of course, their very portability makes them less susceptible to theft.
Car interiors vary in size, shape and configuration, so look for a third-party kit to help support your player while travelling, rather than having it sit loosely on a lap or on the central console.
Some portable DVD player kits are designed with backseat viewers in mind and come with a central playing unit and two separate screens and harness or mounting kit (to hang the screens from the rear of the front seat), plus a games console-type controller with built-in games. These systems can start at around $500.