Hey Rio,
I notice in you're in Scotland - me too! - so hope this might have some practical relevance. If you're in Glasgow or Edinburgh, the city busdrivers do not make change so have the exact amount ready. Don't know about other cities. The more regional services (Stagecoach) do make change, as you long as you don't give them any big notes. Also, if you go to stagecoach.com then you can view schedules and stops. Good luck!