Read past and present essay topics from other colleges: Brainstorming Tip #6
Find the Common App essays too broad? Read other college’s essay prompts. They may spark an idea.
The University of Chicago has great supplementary essay topics every year. A couple of years ago, one topic was: “It Isn’t Easy Being Green” by Kermit the Frog. That turned into a great long essay for several kids I know who never applied to U Chicago. This year’s topics are great as well. One includes, Where’s Waldo? Go to https://collegeadmissions.uchicago.edu/apply/essays/ and read the topics.
Tufts also has great prompts at http://admissions.tufts.edu/apply/essay-questions/.
Perhaps one of the supplemental topics can turn into your long personal statement.