These Eastern Painted Turtles have hauled themselves out for a contemplative basking session nearly every time I ride by the pond at the entrance to the Vassar Farm and Ecological Preserve:
What do turtles think about while they’re basking?
Those turtles are probably relatives, even if they’re in a different pond farther downstream along the Casperkill.
The Smell of Molten Projects in the Morning 
I suspect they are think something along the lines of, “I hope nothing tries to eat me today.”
All of life consists of “Ah-ha!”, “Yum!”, “Uh-oh!”, and “Ho-hum”. They’re pretty far out along the “Ho-hum” axis, but the little ones definitely have their “Uh-oh!” moments…