Wolf Creek Park on Lake Livingston was very nice back in the day when we camped. It may be a ghetto now, and you will need to reserve a spot. Bank fishing and boat rental in the park.
Oh, just remembered a bike ride to a beautiful park just north and east of the casino on 35 in OK. I forgot the name, but it will be nicer and more crowded. It's very popular (Murray?) can't remember.