Rock Island State Park Campground
This is the first campsite we stayed at for Thursday and Friday night during our road trip. The park has two campgrounds. The main campground has 50 sites that accommodate RV's and trailers; some of them accommodate tents. Then there is the tent only campground which has 10 sites and that's where we stayed. Each campground is grassy and has enough room for two tents (maximum of 6 people can stay at one campsite). Each site has a fire pit, BBQ grill, picnic table, fresh water pump and an electrical hookup. If you want to book a tent site I would try to book campground 54, 55 or 56. These three sites have a little bit more room on each side so you'll have some extra space. We stayed at campsite #54. If you want to build a fire while you're there, there's a country store a few minutes up the road that sells locally sourced firewood (they ask you do not bring your own, bringing foreign wood into new areas is not good for the environment) and you're also allowed to pick up anything dead on the ground and burn that as well. We made a fire our second night but we cooked all our food on my MSR WhisperLite Backpacking Stove. We didn't bring a cooler so for breakfast we had peanut butter and banana sandwiches, apples and oranges. I brought snacks like trail mix, fruit and pringles (lolz). For lunch we'd stop somewhere on the road since we were usually out for the whole day anyways and for dinner we brought freeze dried backpacking food.
We really liked the campground and it was a short walk away from the beach and a close drive to see Twin Falls. ALSO, almost forgot, the campground has a bath house with showers, toilets, sinks and even a drinking fountain. We found that incredibly useful after a long day of hiking and gettin' smelly.
For more information on the campgrounds and to book a campsite in the park go here.