Stock in gas drops and gripe water.
On a more serious note, burp cloths. We love the kinds that are made out of the old-school cloth diaper material (sorry I'm not more specific!) and the aforementioned Aden and Anais. The Aden and Anais one is the one I have in the diaper bag, since they can be a bib or a burp cloth, and they're cute, cut well for your shoulder, and absorb decently.