Hi Sid: I'm not a CruiseMates Staffer, nor do I play one on T.V., but I did stay at a Holiday Inn Express last night, and I know the answer to this one.
(Actually, we book GTY a LOT!)
If you don't have your cabin number before heading out to the port, all you need do is ask the porter, when you drop your checked baggage to look up your cabin number, and place the correct tags on your bags. (Actually, you can do this anyway, if you forgot to print, or you just don't like the "new" luggage tags.) The porters have a list of all the passengers, and what cabin they're assigned to, and they have luggage tags that they can place on all your checked baggage.
This doesn't happen often with a GTY, but occasionally it does, and that is the solution.
Have a GREAT cruise!
Forgot to mention. Ordinarily the cabin will be assigned right after final payment is made. It can be assigned anytime between then, and embarkation. We always just check the Carnival Web Page.