The classic La Paz day trip is Espíritu Santo Island, reached by boat for snorkelling, sea lions, beaches, and red volcanic cliffs. It is already protected and permit-controlled, so choose operators who take the rules seriously.
Beach days north of town are easier independently: combine Balandra, Tecolote, and Pichilingue if you have a car, but give Balandra first choice of timing because access can be capacity-limited.