1. How to pack. You no longer bring 15 suitcases when you go on an overnight, because you've streamlined your process. You know that you don't need 15 bikinis and 12 pairs of heels when you're spending the weekend with grandma in Tucson. You know what travels well, and you take just what you need.
2. Stick with a career path, even if it's hard at the beginning. This might not be THE one and only career you'll ever have, but it's the one and only one you are fully committed to right now. You can always go to med school in your 40s if this doesn't work out, but you're not giving up and getting at part time job at Starbucks if things get tough at work. In fact, you like tough.
3. Quit a job if you hate it. But you know the difference between tough and "my boss is a psycho and this is not where I need to be." You have know how to listen to your gut, check in with your head, and make the right decision.
4. Dress according to what YOU think looks good, not what other people think looks good. When you're younger, there's basically one kind of way to be attractive but when you get older, lots of different people are attractive and you've figured out your very own look, and it makes the world a beautiful, diverse place.
5. How to throw a dinner party. No more pizza in front of the TV EVERY time your friends come over. You have a real apartment and you now throw legit dinner parties. That means shopping, prepping, cooking, entertaining, the whole nine yards. Cleaning up, too.
6. How to fearlessly ask for what you want. Whether it's for a salary bump or the birthday present you've been dreaming of, you aren't afraid to put your needs first. You might not always get what you want — ice cream socials every Friday! A pet pig named Harold! A reasonable pay increase! — but you aren't afraid to use your voice to try.
7. Save money. Maybe you don't have a financial planner (yet), but you know the different typed of IRAs and you contribute the max to your 401K. Hey, you even have a little money left over each month, and can lend some to your little sister to buy new heels or a play station or whatever. (Plus, you're smart enough to know you're never getting that money back.)
8. How to say no. You know what you want and need and perhaps most importantly, you know your own limitations. You don't need an elaborate excuse to get out of something, you can just say no. You no longer do things out of guilt or obligation, you do things because you WANT to. Also, you know when to say when. And not only about booze, but also when it comes to friendships, relationships, French fries, etc.
9. That the body you have... is the body you have Love it, treat it well, and dress it in clothes that make it look and feel amazing.
10. Whether or not you want kids. If you're single, this is something you're gonna want to discuss with the new dude you're dating fairly quickly. If you're in a relationship, well. You already know this.
11. How to get home when you're drunk. You know when you're gonna drink and you know if you're gonna drink too much.
12. That you're a different person now than you were at 19. And that's a good thing. Don't you hate it when someone is like, "oh you think THAT now? I remember 10 years ago you said this!" It's like, yeah. Maybe you did eat meat and listen to Sugar Ray in 2004, but ten years have passed and you've grown and matured and become who you are.
13. No matter how close you get with a guy, never neglect your closest most solid friends. Your core group is solid as a rock, and you know these people would walk through fire to bring you ice cream after a bad date.
14. When to make a dentist appointment. And your mom doesn't even have to tell you to!
15. Eat dessert if you feel like it. You know slice of cake isn't going to kill you. As Oscar Wilde said: "Everything in moderation, including moderation."
16. You should no longer care about what the mean girls think. Mean girls exist in the world long after high school, and they are always a nightmare to deal with. However, as you get older and more secure, you can blow off the bullshit and just do your own thing.