A cat carrier or small (but comfortable) cage will do just fine. We exclusively use fleece/blankets/towels for bedding here, but even if you don't, I'd suggest doing so. It's comfy and easy and bedding won't end up all over your car (and it will!). Make sure to have a hidey house/cardboard box for them to hang out in. Some pieces of fruit to keep them hydrated (best not to hang a water bottle since the car will be moving).
Oh and also, i'm picking up 6 rats so I am gonna be putting the 3 adult boys in a dog carrier. But for the little boys do you think that I could use a cardboard box that is too tall for them to climb out of and transport them in that? I'd be keeping the box on my lap of course but does that sound ok?
For travelling, I personally love my homemade rubbermaid bin cage. I only gave them one 'window' of mesh, so it helps protect them for drafts and such for long car direves. They do about 2 hours of driving every month (to my parents' place and back).
I drilled a hole in the side to hand a small water bottle as well, though they tend to ignore it on long direves.
I made it back when I had to keep my two young males, Lestat and Tsume in something before introing them to the bigger boys, and it's held up well in the 2.5 years since. Granted, it's a little squishy for 7....