Well seeing as you can't really buy DVD add on drives for laptops, any recent laptop which comes with a DVD drive will have the spec needed to play them. Simply go to a shop and look at the laptops with a DVD drive and the lowest specification would be suitable.
By "when I travel" do you mean when you're on the move, and using the laptop on its battery. If so, you'll need to ensure that (a) the DVD will work OK without mains power; ansd (b) that the battery capacity when using the DVD is sufficient to allow you to watch a one or two hour movie etc. I suspect that a DVD uses more power than simple word processing etc.