Oak Openings in one of my favorite parks. I've actually completed the 16+ mile hike there, and it's amazing. You feel like you've been all over the country because you've gone through a pine forest, sand dunes, a grassy meadow, and around creeks and ponds.
If you prefer to picnic there are great eating areas, and a nice playground for kids. You can also see horses on the trails there or ride bikes. Love it!