I think you can get by on RCL but agree on the long sleeved shirt with tie. Do check out local thrift stores. There are often high quality suits that have been worn once for a wedding or graduation and cost peanuts. Possibly even just a dark suit jacket to go with the khaki slacks. It is a 4 night Bahamas cruise, so the clientele and dress will be younger and more relaxed. Were you going on a longer Celebrity or HAL cruise, you might feel awkward with no jacket or suit. Have fun........and don't worry about the fashion police on this site or on the ship.