You don't have to be a couch potato just because you have some time by yourself. It's fun to go solo, too.
Hop on your bike (don't forget your helmet!). Take a ride around the neighborhood and see what's going on. Bike to the store and see if there are any new comics or magazines you want to buy.
If you have skates or blades, give them a spin (don't forget your helmet and pads!). If you skateboard, grab your board, helmet and pads, and try some new moves. Try jumping rope and counting how many times you can jump before you miss–jumping rope is a really great way to get aerobic exercise (the kind that makes your muscles use oxygen and your heart stronger).
Sometimes being by yourself lets you practice things over and over, which you usually can't do when you're playing with somebody else. Plus, you can work on your technique so that you'll amaze your friends when you play with them again!
If you play tennis, try hitting a tennis ball against a brick wall. Count how many times in a row you can hit the ball without missing–then try to beat your own record. If basketball's your thing, try shooting hoops and seeing how many foul shots you can sink. Or if you're into soccer, grab a ball and see how long you can keep it in the air using your feet, knees and head.
More things to do when it's just you: