K.F.
I have a 3 year old as well, and stressed about the same thing as both my parents and my husbands live a distance away. I have kept a small training potty in the trunk just in case, and in the past 6 mos she has only needed it once. Otherwise we've stopped in at Mcdonalds, ect if we can find one. I have found that my daughter can actually "hold it" much longer then I would have thought, and we rarely have to stop. Good luck!