Your life is about to change. Everything you have known for the past 18 years will disappear in the blink of an eye. You graduated High School and you are about to start your last summer before adulthood hits you with a stick. You need to enjoy your last few months with your 'best friends' before you move away to meet the people who will become life long friends. Coming from a student who just finished their first year of college, these are the things you need to take advantage of before you leave.
Summer is all about the freedom of no school and no responsibilities, once you hit college all of that changes. The people you have grown up with are about to go their separate ways and you need to cherish every last moment with them. Once you start college, you will meet new people and the people you used to talk to everyday just become an old memory of the past. Go to the bonfire. Go to the sleepover. Go to the going away party. This is the last summer to truly be a kid. Enjoy the presence of your friends because once you come back everything will be different.
Spend time with your family. No one wants to sit and talk or hangout with their parents, but you're leaving the nest, your parents want to spend as much time with you before you move out and no longer need their help with everything. Go grocery shopping with your mom, or help dad with yard work. It is the tiny things that matter most when it comes to parents. Most importantly, sit down and have the homemade dinner your mom made, appreciate it before you are stuck sitting in the dining hall eating food that will result in hours on the toilet after you eat it.
If you have younger siblings, spend as much time as you can with them, because once you come back they will be grown and different and not be the same little brother or sister you saw them as before. It will be just as weird for them as it is for you when they leave, they have known you to be there everyday since the minute they were born, the person they look up to will no longer be down the hall anymore.
Get a job. Any extra money going into college will help, because once you run out you are out of luck. Getting a summer job with your friends can be a lot of fun and you will be making money and memories on top of that.
This is the last summer that you will be able to enjoy with your closest friends before you all leave for college. Cherish every moment because the summer after your first year will be completely different then this one. Once you come back your no longer the 'kid' you were before. You'll have responsibilities and adult things to take care of, so enjoy the fun while you can.