We discovered Nike Ceso sandals/flip flops last summer. Most comfy shoes I've ever worn to the parks. Kohl's has them for $20 not on sale, and on sale as little as $14.
I had originally bought them to wear to the pool, but ended up wearing them to the parks the first day of our trip, and never once wore my sneakers on the trip. Bought some for my dds and they wore them all summer and then on our trip this fall to DL.
Just picked up new ones for our Spring Break trip.