Not quite discworld related, but close:
Mystery cat takes regular bus to the shops
Bus drivers have nicknamed a white cat Macavity after it has started using the No 331 several mornings a week.
The feline, which has a purple collar, gets onto the busy Walsall to Wolverhampton bus at the same stop most mornings - he then jumps off at the next stop 400m down the road, near a fish and chip shop.
This reminds me of the travelling cat from Terry's The Unadulerated Cat.