Myself and many other hosts offer extra things that some prospective guests might need and/or might take advantage of. These things include ground transportation to/from the airport, adding a full breakfast to booking, ordering groceries so they are onsite when they arrive, etc.
Right now there's no way to offer these and pay for them via airbnb. It would be an easy way to give guests a better experience, and a chance for hosts to make a little bit more money.