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WE "did" Singapore in one day from the ship using public transport. Using a guidebook plan your day and it is possible as the ship docks very close to the city. The port for Bangkok is about an hour and a half by road from the city (I think) so don't know how feasible that would be without arranging a private driver. Can't help with the other places - sorr.
It is easy to DIY if you do enough research. Try this site: