Go to the loo. Possibly Read a book/newspaper/phone. All the time in the world to relieve oneself and catch up on some me time.
Feel the urge to wee but inevitably have hands full of baby/baby related things and decided to hold it in until a spare minute arises. It never does so after 3 hours of growing your bladder to bagpipe proportions, you either sneeze and your pelvic floor betrays you or you run to the toilet as fast as humanly possible. All doors are left open, a baby monitor is handy to have on particularly long visits to 'the throne' and in real emergencies, baby is treated to a one to one audience of the whole thing. Add a cat asking for food or climbing onto lap out of desperate attempt to recoup attention lost since non furry baby arrived and you get the full picture!
NOTE: On the upside, public bathrooms are now more comfortable because having the convoy of buggy and baby with you entitles you to the disabled toilet facilities as they inevitably coincide with the baby changing area. Bring on more space, more privacy and a hand rail that helps weary bottom off of loo seat.