If you're looking for more stationary training options, consider creating a circuit of body weight-based exercises. Beach yoga is soothing, and there are often groups you can join if you don't like to stretch solo.
For those who feel the need for weights or props, kettlebells or medicine balls can serve multiple purposes at the beach. You don't need too much gear, so make sure you bring weights you can use for multiple exercises. We're sweating just thinking about medicine ball burpees on the beach! Other exercises pack more oomph on the beach, due to sand resistance. Walking deep lunges, sumo squats, and pushups are all going to offer their own challenges on the beach. Have a little fun and mix it up!