Visit those fancy rooftop bars :- I suggest Above eleven , Sukhmvit 11
If you haven’t taken river cruise then Chao Pyara river cruise can be done You can sit at River front of bangkok Or just do shopping at Mall
Visit floating market and Buddha Temple's during the day time Do Clubbing at Night or Nana Plaza If you want to 🤫 or you can Do Night shopping in the street. Next day you can go to MBK mall also it's an Huge mall for Shopping
Bangkok is quite lively during the night. You can go to Khao San road to party your night like crazy. Or you can go to Nana Plaza, Cowboy Soi etc if you are looking for adult fun. You can also visit the Sky Bar which gives a 360° panaromic view of the entire city.