I like carts that have an organized spot for some tool storage mainly
drawers like these. Having key tools with you is a nice benefit and I've seen a few teams who've had enough drawers on their cart that most of their hands tools are always with the machine.
I'm a big fan of carts like
4564. Large tires for transporting over obstacles, a spot for the driver station, several drawers for tools, and a nice sized area for the robot. Don't forget about a spot to throw an extra battery or two.