Rabbit feces and urine are both quite difficult to get good, clean samples of without being at the vet’s anyway – it might be a good idea to bring in a few of your bunny’s poops to show them to the vet if there’s something “off” about them, but other than that, it shouldn’t be needed. More important, I think, is that you’re prepared for the journey to the vet with your bunny. In his/her carrier, you should have fresh hay and some warm blankets (if it’s cold out) and maybe a frozen water bottle and a blanket if it’s hot out. In addition, I always take a few of my bunny’s favorite treats along, a bottle of water, a syringe and a small bowl, in case of an emergency while transporting (car breaks down, rabbit needs to drink but is too nervous to, etc…).
Be prepared! With a normal check-up, I think it’s just important to worry about the transportation. The vet appointment itself will go smoothly, and probably won’t require anything in particular from you – just your bunny and your knowledge about him/her! 