Even on supported rides with rest stops I always take the same stuff with me as if I was riding alone or in a group. This way I can usually have a flat fixed and be on my way before the SAG wagon shows up and it prevents any gastrointestinal distress mid-ride should something at the rest stops not agree with me. Occassionaly the stops will have things I normally eat, other times they don't and I eat what I brought. But I will usually take a couple of things from the stops to try on my own time for future reference.