As far as I understand it, you actually have to get a visa or ETS to transit the US, don't you? In other words, you will actually enter the US as a tourist and not just stay in a sterile area in LAX, right? As long as that is the case, it will be very easy for you to go to one or both of those of stores. They are very close to the airport. (I guess you just need electronic authorization since you are from UK.)

We don't have anything like a VAT here, so there's nothing like that here.

search for los angeles taxi fare finder or something like that. It's probably around $20 or less to Manhattan Beach (plus tip, ~20% is good.) You can get a card from the driver and have the store call you a cab when you are ready to leave, or just pay the guy extra to wait for you.

-David