So you have a friend who is going to spend some time traveling and that journey includes the United States. Usually you would buying him a travel guide.
But our times require something different. I recommend that you send your fiend the link to Professor James Duane talk entitled "Don't talk to the Police".
In a country where habeas corpus is no longer controlled by the court system, those 26 minutes could save your friend a lot of trouble (as confirmed in the follow up presentation by a police officer).