On my birthday, I invited my classmates and colleagues to have dinner in the hotel room and prepare to buy a cake. What should I do? Take the cake away? What are the details?

Go to the hotel you want to go to and book a room with the front desk. Then take the cake to the hotel or send it to the hotel after eating. If you like, you can talk to the place where you bought the cake and the hotel. Their job is to serve you as a consumer, not to make you beg them.

When booking a room, the hotel should find out the cost and whether drinks can be brought (the cost will be much worse)

And then it's almost straight. It's normal to make cakes by yourself now. You can give it to your good friend to help you, so that you can greet other friends.