Buckets with good handles (safe, secure, comfortable to hold full of sand, water, water and sand).
Battle ropes, extra fun to swing side to side in sand and they can take some serious sandy abuse.
I like the pillow case idea as a quick cheap option, but I like duffle bags as a sturdy reusable option personally.
take some empty bags and fill them up for a warm up then use the sand bags for your workout. Bands can go anywhere as well.
Between some sand bags and bands you should be able to do a pretty good boot camp workout.
You could also buy some empty 5 gal water jugs and fill them up for farmer walks on the sand..that would be a great workout.
Here is my beach bootcamp secret. Have each member bring a pillow case. They can fill it an appropriate amount of sand weight for their level. Tie a knot and let the lunges, presses and pain begin!
It you have access, kettlebells and medballs go a long way on the beach!
And that doesnt wokr there are endless bodyweight exercises when performed with proper form will kick their asses! Good Luck Coach Briody