A pen is best for the first month.  This helps a bunny know his area and develop good litter box habits.  There is a plastic mat for his water bowl and lettuce.  A small bowl for some pellets, and cardboard to play with and chew.  For a big bunny, you will still want to let him/her explore every night for exercise.

Example of litter box set up.  Putting hay in the front helps them to want to use their box and maintain good habits.  Some use natural paper bedding or wood pellets for the litter box part.  Tiny Bunyah never relaxes in hims box, but this day, the clean paper bedding must have looked extra soft.  :)

For the bigger bunnies, you can use a paint tray (as shown above).