Long Beach is a great place to fly with lots of interesting focal points.
Down at the Pike there are two large parking structures, if you park on the top floor you can great reception with little to no interference from other buildings. Taking off is a bit tricky because of all the rebar in the concrete so you get some magnetic interference at take off and landing.
You can drive down to the Queen Mary and fly from there. It's very open and you can get the same focal points.
You can also drive down Ocean Blvd and find a place to park literally anywhere between downtown and the Belmont Pool. This is great if you want to get beach footage. Look up the "100 days of summer" calendar from the City of Long Beach to find out if there will be beach events. You may or may not want too many people in your footage, it depends are what your after.
The police don't usually hassle you. Fly smart and fly safe to avoid any questions or phone calls to the cops about disturbing the peace.