Hello S.,
The first thing that we do while traveling is to limit our daughter's drinks. So, we give her a quick drink of juice and then keep the sippy cup in the front seat with us.
The second thing that we do (on road trips) is stop every 2-3 yours for a potty break. Public toilets are disgusting, so we use the portable "Fisher price Planet Froggy Potty Seat". It's perfect because we keep it on the floor in the back seat and she can sit down out of everyone's sight and potty. The down side to this is that you have to pour out the pee so we typically park near the grass. (embarassing- yes....convenient and clean - yes)
As for the hotel, they do not have children's seats so we do two things: first we keep the portable Fisher Price Frogy seat in the hotel bathroom next to the adult toilet. The second option is to bring your own soft potty seat cover for the adult toilet.
Fisher-Price Precious Planet Potty --> http://www.amazon.com/Fisher-Price-Precious-Planet-Froggy...
Potty seat cover --> http://www.amazon.com/Disney-Pooh-Soft-Potty-Seat/dp/B000...
Best to you,
Christina