What sort of combinations of pets can people keep together in your runs?

This would depend on the size of the run and the quantity of animals. Chickens and ducks can easily be kept together in the same run, but would need different houses to sleep in as ducks do not roost in the same way as chickens do. Rabbits can also be kept in the same run area as chickens but rabbits and chickens have different needs to keep them happy and healthy, so you'll want to ensure you can balance the two.