Get sunburned
If there was only one thing I could make you suffer through right now, a big, bad, sunburn would be it. The pain of a sunburn is unignorable, and relief comes slowly. Everything else I will tell you is easily disposable, and easily ignored. But I will tell you anyway.
Enjoy your time as a young person. Get your kicks while you can, because once you get old, the party is over. Those members of the opposite sex in your age group not yet married will be in pursuit of conquests much younger than you. When you are 30, the only people attracted to you will be 50 year olds. Roots... are ugly.
Don't worry about the future. The future is more painful and sad than even your worrying brain can understand. Spend more time on the Internet. The problems you face on the Net can be solved by flicking the power switch. They are the only problems you will have that are solved that easily. Bathe.
Go ahead and get as many people into bed as possible; as long as they're not drunk or thirteen years old, any problems they have the morning after are theirs. Not yours. Smoke 'em if you got 'em. Spit.
If someone tells you to stop wasting your time on something you enjoy, tell them to eat it. When you are lying on your deathbed, coughing up blood and feeling everything but your legs, do you want to look back on your life and see a series of accomplishments that benefitted people other than yourself and assignments you didn't want, or times you spent playing frisbee high on LSD? I thought so.
Your problems are bigger than you are. So run underneath their legs, grabbing their balls and twisting as you go through. Rake your leaves into the neighbor's yard.
Just buy the damn thing.
Don't get married, or marry, knowing that a person with a wedding band on their finger is uglier to single people than Justin Timberlake after getting trampled by a herd of bison. Never mind the bollocks, here come the Sex Pistols.
Yell out loud in the library. It's the only place where your words are bound to attract attention. Lick it.
Ask every friend you know if you can borrow ten dollars. If they say no, they're not really your friend. If you have a lot of friends, you'll be rich. This is the premise behind the entire collegiate Greek system.
Live in Texas, but leave before you start wearing cowboy hats and foot-long belt buckles. Live in Detroit once, but leave before you start looking forward to riots. Travel to foreign countries. The rest of the world hates Americans, so you can act like a pompous asshole and get away with it.
Certain things will be true no matter what: your parents will wish you did something different with your life. The only Platonic friendships you will have with the opposite sex are the ones you don't want to be Platonic. Despite this, you will want to live to see another day. Don't focus on the long-term goals. You will never meet them. Think about the date you have on Friday, the movie that comes out next month, the possibility your sports team has of making the championships next year. They may be trivial, but they're all your have.
Just that and a sunburn.