I've ridden on Megabus before, and the double deckers I was on still had a big cargo compartment or two in the back. They did fit bikes, and I did see one full, not-in-case bike in the compartment. I was curious, so I asked the driver about bikes. He said that if there is space, they can put the bike in there, but it all depends on how many seats get sold on the bus. So, you might be able to bring a bike to somewhere, but not necessarily back.