Assuming you'll be using credit card, please do let your credit card companies know that you will be in USA, so they do not reject or deny charges you try to make while in USA.

If credit card company asks for the dates you will be in USA, give one of your credit cards a leaving-USA date a few days later than planned, so you have a card that will work if you get delayed leaving USA.

If you're in LA, but don't have car or friend near the ocean.....a good splurge could be a night or two at a hotel within walking distance of a nice beach!

The "Lonely Planet" guide for LA has quite useful info.