Driver license is sufficient.
Just your I'd and that's it .they are okay with that.but make sure you pay attention to your bags that go under the bus because me and my daughter got on the bus right there in Orlando and was told that they had my bags got to first destination and my bags were not there .I had to almost 3 days after I arrived at my destination for my bags.
I used the reservation I made online printed out with me, and had a hardcopy of my passport just in case, they didn't need the passport copy though
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