As long as it's obvious from the context, you can say "Ticket" when you're talking about your bus ticket, too. It's more common to say "Fahrkarte" for all kinds of tickets for public transport, though.

Danke

"Fahrkarte" is more specific, and only used for tickets regarding bus, train or any other "rides". "Ticket" is much more general, and can be used like the English equivalent for almost anything you need to buy a ticket for.