Remember that your list is a list of characteristics you want the college to know about. It's a list of personal strengths and talents. Qualities that recommend you for inclusion into a group. It's not resume items or things you've accomplished.
When a student says "I'm writing about my trip to France" I worry that they are thinking that colleges need kids who've been to France. WRONG.
Colleges need students who are thoughtful, creative, energetic--they need enthusiastic organizers, curious researchers, and open-minded thinkers--young people who will test and challenge the ideas around them. So fill your list with personal characteristics and then find a lens through which your reader can see one of them.
In the end, the essay might tell something about your month in Aix, but your topic should be your enthusiasm or your flexibility or your insight. Whatever events, incidents, or conversations you write about should illuminate who you are, not what you did.