Like another person said, you'd probably be best off with a power inverter. This will convert the 12V DC "cigarette lighter" socket in your vehicle into AC power. I was in a pinch a few weeks ago and Wal-Mart was out, Walgreens had one in their automotive isle for $50, it's a 400W (800W peak) inverter with both a cigarette adaprter and battery aligator clips. However, my needs were for more than just my Panasonic portable (I have one of these, too). The smallest thing you can find at *-Mart or wherever should suit you fine. $20 is a reasonable price for a 100W or so power inverter!
With the power powerful units, you can hook up multiple devices (like televisions, power tools, etc).
Keep in mind that these devices produce "square wave" electricity instead of standard sine waves. This will probably not be a problem with these expensive electronics (like your DVD player) since they have better AC adapters. However, with cheap boom boxes and/or radios that have crappy power supplies, you might hear buzzing from the speakers or poor sound quality.
-- Robert