There was NO way we were fitting our dog and all the belongings we wanted to bring without more space than we had.  We had to add to our hauling capacity without going too nuts so we made a few purchases:

-21 cubic foot cargo box

-Railgrabs and crossbars in order to mount the cargo box on the roof

-Bicycle rack with a four bike capacity that mounts to my hitch (we traveled with 3 bikes).

We purchased all these items from Yakima and are very satisfied with the product and customer service from them.  A well known competitor is Thule. 

Worth mentioning is an AWESOME Kelty brand collapsible cooler we’ve put to good use.