Example 1
I think I'm going to puke!
Blame your brain's bilateral vomitation center. It notices when your stomach is upset and makes the final call about whether or not you'll barf. Here, an exclamation point is appropriate because the speaker is expressing urgency and alarm.
Example 2
Oops! I did it again.
Interjections, like Oops, often take an exclamation point since they're used to convey strong emotion.
Example 3
Anthony's mom called after him across the schoolyard, "Honey, don't forget your Garfield lunchbox!"
In this humiliating example, an exclamation point is correct because Anthony's mom is yelling at him. Note that when a quotation ends in an exclamation point, it's placed inside the quotation marks.