If you're just applying to work at a store you generally won't need a resume, they'll just have a standard job application for you to fill out. Writing a resume won't hurt, since you'll need to write them later anyway. Until you graduate college and have been working for a couple of years you should keep your resume at about one page. It couldn't hurt to have a cover letter but you should customize them for each place you're applying to. I have a cover letter I've written but out of all the jobs I've ever interviewed for or applied for by email, nobody has ever asked for a cover letter. Generally the kinds of questions you'd answer in a cover letter get answered in an interview.
If you want a template you can use mine:
http://db.tt/9qFx76wzNote that for education, if you haven't graduated college yet then you should list your high school, graduation date, GPA, etc for that. If you graduated from high school in say the past 2 or 3 years, you could list activities from high school as well. "Activity" at the end refers to any non-school related clubs you might be in - scouts/4h/boys or girls club/rod and gun/etc. Don't list your gym membership or that you like hiking, although something like "completed the Appalachian trail" would be worth listing since it's a significant accomplishment.
