1. Always be prepared.
2. Even if you think you are kind of strong and that your friend is super little, you probably can't bench press her. Trust me.
3. Don't bring cookies. Unless you want to drink 1.5L of white wine and eat said cookies.
4. Your skinny friend (referenced in #2) might try to convince you that you can improve your core strength with some simple Pilate's moves. Don't try them.
5. In the end, the best core workout is laughing your ass (and ab flab) off with friends.