Cover all the Wats in the map. Some famous wats are Wat Mahathat, Wat Ratchaburana, Wat Phra Si Sanphet, Wat Yai Chai Mongkol, Wat Choeng Tha. some wats have an entry fee of 150 bahts like for e.g. Wat Mahathat.
There are places to see elephants as well, the map will direct you very easily to these places.
Try the food here, really authentic. Get you camera charged, there are a lot of places to be shot. Wear shoes, there is a lot to walk.
There is a night market here which is very close to the station, a good place to pick up souvenirs :)
The last train is at 7.05pm for Bangkok, you can decide to stay here and catch the sunrise as well.
Have a great trip!