Is it safe to leave bags on the beach while surfing in Unawatuna.

Leaving highly expensive valuables completely unattended on any busy public beach anywhere in the world is universally a terrible idea. While Dewata beach is incredibly friendly and violent crime is nonexistent opportunistic petty theft of a visible smartphone can absolutely occur. Your best perfectly secure strategy is to officially rent a surfboard directly from one of the highly reputable established surf schools lining the sand. They will happily store your backpack securely locked safely inside their main office behind the counter while you surf the waves.