really... nice to see that someone else sees value in flyover country!
Oklahoma in general is quite laid back. That being said, we really don't have a great deal (that I'm aware of) of a night life. Activity around here really tends to die off around midnight, you won't see many people out at all around then. I'm quite the homebody myself.
I don't know your fondness for lakes, but there are several here, and they're all really good places to just hang out. Lake Hefner in NW Oklahoma City is fantastic for sailing, kiteboarding, and windsurfing, and it's kept quite clean, at least from the parts I've seen. One thing in Oklahoma that we don't lack is the wind...
A couple other things come to mind: South of OKC is Norman, and east of there is a little place called The Little River Zoo. Not much of a zoo, really, but it's more along the lines of an animal rescue. Everything from Desert Foxes to Brown Bears. If you're into the really big cats, there's a big cat rescue to the west called Tiger Safari. nice place.
Couple of art museums, Cowboy Hall of Fame, and the Myriad Botanical Gardens.... that's all I can come up with off the top of my head. But then again, I live in NW Oklahoma City, and Tinker is more SE. I don't venture down that way too often.
One last thing: I don't know that all locations do it, but if you can find a place called Hideaway Pizza... they're fantastic. In addition to fantastic pizza and hot wings, they will give something along the lines of a 50% discount to military personnel who are in uniform.