Most offer parking and changing facilities. Some have camping facilities, some have cabins and a few have new, two bedroom, villas . Seven Seas Beach campground near Fajardo. Even so, you should judge the situation yourself, because conditions change. Beaches are very crowded in the summer, especially 3-day weekends.
Winter is much quieter.
ACC Autoridad de Conservacion y Desarollo de Culebra administers the Flamenco Beach campgrounds on Culebra Island. Highly recommended for safety, facilities and the most beautiful beach. They usually accept walk in reservations in the winter months. Summer, especially summer weekends, are zoo-like. Need advance reservations.