For example in Bingley (Yorkshire) where my mother lives, and in Southampton (on the South Coast) where I live, the buses use ITSO smartcards. But you can't take a ride on her bus with my smartcard.
Contactless bank cards do work on both systems though, and on the London transport network. So "Use a credit card" ends up being the "one physical token" solution.
Even if I put some money on that card, via her bus' payment system? As in, I go to a tfl ticket machine, touch, put money on, touch again and then I can use the card on the underground. Then I go to Southampton, go to a ticket machine, touch, put money on, touch again, then I can use the card on the Southampton's transit system.
Literally just tried this with the Southampton card in London against a tfl machine. No Dice.
Shame, but yeah, not really surprising.
Baby Steps!
Just two weeks ago I was finally able to get an oyster-like card from South West Rail that works with the train and the tube. Progress, finally!