Well, as the others have said, you can leave the tray empty and clean it daily.
In my case, that is not possible because I may receive a call from a client at night (when I am at home) and not have the time, or possibly forget about the tray, so I use bedding. What I use is yesterday news, just a shallow layer on the bottom tray, so they can't reach it.
Most cage beddings are ok, as long as you don't use wood shavings, or scented bedding.