It all depends on what's on your itinerary!
The beachhouse has running water with separate men's and women's shower rooms and toilets. If going near the beach, make sure your camera is kept protected from the water. Not that the waves are like oceanic tides, but when the speedboats cruise up and down it, they can build and spread quickly. If you're going camping around the reservoir, I recommend mosquito repellent. First and foremost, though, check the weather forecast. If rain is a possibility, a tarp and some rope to tie it to nearby trees or stake in the ground around the tent can really help keep things dry. If you're going to the beach for swimming or sunbathing, some suntan lotion, a towel, a lightweight beach chair, small cooler-- pack light because there is a little walk involved between the parking lot and the beach itself. Although there are picnic tables under the trees along the way as well. I recommend sandals to protect against the heat of the sidewalk and the sand (which can be uncomfortably hot and hard feeling to bare feet). It's not like soft white sand dune sand. It's pretty rough stuff.