I'm not a Californian, but Mattes said just what I would have about tipping: 15-18%. (No idea about bar drinks though.) The rule used to be 10-15% fifteen or twenty years ago, but inflation has taken its toll, and while 10% may be in some sense still the minimum acceptable, it's no longer common at most restaurants. However, I wouldn't hesitate to tip less than 15% for poor service, and I still find 20% rather shameless to expect for normal service, though nice for service beyond the call of duty.
There are polite and impolite ways to talk about sex, politics, religion, and money, as with any topic. After you get to know people a little, if everyone can stay friendly and open-minded, it can actually be refreshing to get beyond small talk. Some Americans might be genuinely interested in what Europeans think -- and they won't often get the chance to find out person to person, so it's not necessarily bad to widen their horizons. But stay tactful and avoid unflattering generalizations. Remember, you may be the only ambassador for your country that many people ever meet.
For some safer conversation ideas, try asking for information, like explanations of American sports or schools or idioms, or ideas for interesting things to do and places to see in your area. People are usually flattered to be asked, and it's a good way to avoid asking personal questions too quickly.
Agree about allowing people their 1-meter circles of personal space, about always saying 'Excuse me' if you accidentally bump into anyone or need to reach or walk past someone, and about asking if you're not sure whether there's a line. ('Sorry, is this the line?' 'Excuse me, are you in line?')
At shops and restaurants, the employees usually greet the customers first, and the greeting isn't such a big deal. But saying 'Please' and 'Thank you' is: 'I'd like the _____, please'; 'Excuse me, could we have some more bread, please? Thank you.' In fact, whenever you ask someone to do something, it's polite to use 'could' or 'would': 'Could you see if you have this in a larger size?'; 'Would you mind turning that music down a little? Thanks so much.'
One more tip: When you call anyone on the telephone, always give your name ('Hello, this is Buzz Schmidt'; 'Hi, this is Buzz') as soon as the other person says hello. In English it's the responsibility of the caller to identify him- or herself.
And a few language tips:
> I'll be taking part in a language trip / I'm going to take part in
> that I should pay attention to
> I'll be staying at Cal State Long Beach / I'm going to stay at
> I'm really looking forward to it / to everything!
> Thanks to everyone for their comments / to all of you for your
Have fun, and tell us how it goes. And if you have the chance to go north and see some of the coast, take it. (-: