Like Sonny the King, I usually go to an upscale hotel. Check my bags with the porter, tip nicely. The best idea is DON'T try to explain your days worth of activities. The porter is just there to handle your luggage. If you tip they will take your luggage, you do not need to be checking in somewhere. Some folks want to wander the beach, others want to see the sights. If I was in Miami, which I will be soon, I would either go to South Beach in a taxi, or try the Holiday Inn by the port and go shopping at Bayside. A few bucks will take you a long way.
