If you want to be guaranteed a welcome at beach, pier and lounging-pool in a super-fun location consider a trip to Rojo Lounge --- the place is purpose-made for day-trippers to enjoy. You will find fab bar-food in a beautiful environment - and as a food and/or beverage customer you are not only welcome but encouraged to enjoy the surroundings.
I can make a long list of resorts that are primarily aimed at hosting overnight guests, so don't just rock up and expect all of them to serve you. If they look "private", assume they are.