You won the lottery: Pay off all my bills, share some money with my friends and then take a long relaxing cruise around the world.
You caught your BF/GF is cheating you with your best friend: That's happened to me before. I dumped his ass and I wasn't friends with my "friend" for the next three years.
You saw someone hitchiking on highway: There was a day when I would pick hitchhikers up, but not anymore. Did you ever see the episode from Six Feet Under entitled "That's My Dog"? Frightening! It's not safe to pick people up anymore. If they really look like they need help I would offer to make a call for them but I wouldn't let them in my car.
You caught a friend stealing from you: If it was the first time I'd forgive them. If they did it again we probably wouldn't be friends anymore.
You witnessed a murder: Call the police.
A random stranger offered you ice cream: Refuse it. I'd thank them but I'd refuse it.
You learned your best friend has a crush on you: That's happened before too. I don't think it is a good idea to get romantically involved with a best friend. Chances are the relationship will not work out and then the friendship might be ruined.
You found a wallet without an ID and fully loaded with $$$$: I'd probably take it to the police. I don't think I'd feel comfortable keeping money I knew wasn't mine. I'd keep thinking about the person who lost it. They may desperately need it.