Definitely would not put anything else in, because there is always a bit of fat in the liquid that gathers at the bottom of the dish.
What I do is to use the screwed up foil which has already been mentioned, or an old carrot cut into chunks (you are not going to eat this!!) so that the chicken does not sit on the bottom of the dish, put a little boiling water (no more than a quarter of an inch) in the dish, and then put the chicken in upside down - that is, breast side down. That way, the juices flow downwards into the breast instead of away, and it is moister.
What you will end up with is a very tender and tasty chicken (too tender to carve - it will fall apart!) and some liquid at the bottom of the dish. Pop the liquid in a bowl in the fridge and the fat will rise to the top and you can spoon it off and throw it out. The stock (it may turn to a jelly in the fridge) can be used for a gravy or a sauce or whatever.