I will bring a tarp, put towels or fleece on top, then the pen. My pens are NIC grids. You can then have a litter box, toys, and other items.
Since you are staying for a few nights, I would suggest finding a hotel with laundry, some have machines you can use. A nearby laundromat can be good too, but in the hotel is more convenient. This allows you to wash bunny stuff so you don't need to take as much. 1-2 towels for the carrier and 2 sets for the pen should get you through the journey if you can wash daily. If your rabbits will use the litter box reliably, then you might not need to do laundry as much. It is still good to have a fresh towel for the carrier for each day though.
Make sure to bring pellets, hay and litter with you. Veggies are easy enough to find and it can be better to buy them as you go. Bring extra since you may use more as you go, cleaning daily does use it up quicker.
Bring cleaning supplies. Several plastic bags. You can stick the litter box in one if it isn't too dirty. A dust pan and brush as well as a rubber brush is good to pick up the hay. Paper towel is good to have as well. Any other cleaning stuff that you use on a daily or regular basis is good to bring.