I use a
1x2 fabric drawer with a fleece blanket on the bottom and one covering half the top (so they have a dark area to hide under). They sell them at Target. I've also put together a 1x2 mini-cage with cubes to use. It's easy enough to carry, but you have to put something thick down on the bottom so the cubes don't hurt they're feet.
If it's a long car ride you should bring some hay and some water covered veggies. They may be too scared to eat, but it doesn't hurt to give them the chance.