Image via WikipediaBecome a critic.
Do you like to go to movies? If you spend a lot of time at the theater during the summer, try writing reviews of the movies you see. What did you like? How does it compare to other movies you've seen. Think of all the aspects of a movie such as directing, acting, editing, art direction, and special effects.
Perhaps you would rather rate music. Write a critique of the top 10 songs. Again, what did you like? Consider the lyrics, the style, melody, and the instrumentation. How does it compare to other songs by the same artist. If you get a chance to go to a concert, write a review of your experience.
Maybe food is more more to your liking. Whenever you eat at a restaurant, write about it. How was the quality of your meal? What about the service? Was the restaurant clean? Did they have a full menu or just a few offerings?
The writing experience helps you practice your written communication skills. It can also help with your vocabulary, spelling, punctuation, and grammar skills.
If you're really brave, submit your reviews to a local newspaper. You never know, they might publish them. If not, that's okay. The writing process will still help you maintain your skills for next school year.