Also, for USNA purposes, one does not necessarily need to "build" an "impressive resume." IOW, I don't think USNA is more impressed by someone who travels abroad to help the needy than someone who stays home and works at a fast-food restaurant.
There are many, many opportunities wherever you live. Find something that interests you and, to the extent you can afford it financially, something that builds on your skills (e.g., sports, science) or furthers activities you already do (e.g., scouting, politics, acting, music). Or just do some good in your local community. I've seen candidates do everything from sports camps to working in Korea with veterans' groups, to an internship on an oceanographic research ship in the Med, to finishing their Eagle Scout project to working at a camp for special needs kids, to working for a landscaping company, and on and on.
The above does NOT mean that you can't take some time off for vacation or just take a couple of weeks to "hang out." No one is looking for you to account for every moment of your summer. Rather, you should be able to talk/write about something you did to occupy your time.