Play at Blissful for free. Have a cold beer or pastis while playing. The court is floodlit, to allow play morning, afternoon, or evening.
There are lots of durian farms on the way to Teuk Chhou Rapids. It may be hard to communicate to a tuk-tuk driver that this is what you want to see, but a tourist office / travel agent can help you arrange it. There don't seem to be organized guided tours like for the pepper farms, but you can go to a plantation and ask for permission to look around – before you leave, buy some fruit as a thank-you. Even when durian is out of season it's mildly interesting; in January you can see the unripe fruit starting to grow.
Stand Up paddleboarding, SUP lessons and tours. Kayak rentals, swimming and cafe.