When I pack I usually toss a skirt (one of those light weight, longer, wrinkley material types) and a nice tank top. Pair it up w/a nicer pair of white flip flops (as others mentioned, avoid the cheap shower shoes) & some jewlery & you are good to go.
Nice thing is the skirt won't need ironed when you get there.
I wouldn't wear the tank that day (too sweaty) but after your nice dinner night then you could wear it some later day in your trip.
And plain white flip flops work w/almost anything so they get worn a lot & probably would have been packed anyway.
That combo give you a cool outfit that is also a little nicer than the average vacation wear outfit but doesn't add to much more to your suitcase (and w/how the airlines are charging & watching luggage now days every bit you can save helps).