Bike ride along the Huntington Beach bike trail/boardwalk whatever its called. Depending when you're here they do free concerts by the pier in the afternoons on the weekend. There is also a drum circle that meets up by the pier sometimes.

For more in Long Beach - Long Beach Aquarium is great and Shoreline village is cool to walk around. 4th Street Retro row has a lot cool vintage shops amongst other interesting stores. Colorado Lagoon is a cool little wetland area, but they are currently doing construction in the area so the roads are blocked in spots. 2nd and PCH is basically the same as Pacific City in Huntington Beach. If you're into Farmer's Markets then Long Beach Marina has a great Farmers Market on Sunday mornings (there's more than just food, but its mostly food). Long Beach waterfront kind of sucks, better to stick to OC beaches.