Most games require at least two people to play or are more fun when played with someone else. If you have some energy and nobody is around, try playing a game with a ball by yourself to enhance your skills in a variety of indoor and outdoor sports.
When you're practicing by yourself in between basketball games, create some games for yourself to not only help you practice but keep game strategies fresh in your mind. Start by standing in one spot on the basketball court. Shoot and make as many baskets or layups as you can and designate one point to each successful basket. You can mentally note the baskets made or bring a pen and a pad of paper to write the score. When you miss a basket, move to another position on the court and practice shooting from there. Another option is to draw a map of the court and mark it with X's to designate previous shooting spots.
If you have access to a football field, soccer field or large grassy area, try this football game for one player that helps develop kicking and passing skills. Set up a kicking tee and place the football on it. Kick the football as far as you can while practicing proper kicking techniques (rather than just aggressively kicking the ball). After you kick the ball and it has settled, begin throwing the ball back to the tee, making as many throws as necessary. When you throw the ball past the tee, place it back on the tee and kick again. If you just want to practice kicking, practice punting the ball back to the tee instead of throwing it. The goal of this game is like golf, in that you want to get the ball by the tee (at least within two feet) to make "par." Give yourself appropriate par goals depending on how far the ball is from the tee, but always shoot for "hole-in-ones."
Before you begin a set, practice ball control skills with your racket. Start with an underhand grip and bounce the tennis ball on your racket as many times as you can without letting it bounce off and hit the ground. After the 10th bounce, switch to the overhand grip. Switch grips after every 10th bounce. To make the game more challenging, switch between overhand and underhand grips after every bounce. After 100 points (or 100 consecutive bounces), throw the racket back and forth between your left and right hands and see how many consecutive bounces can be achieved. For each consecutive bounce, give yourself two points.