Just remember, whatever you put in the resume will be open to question durring any interview. The first thing I'd ask as an interviewer is, "With your desires changing constantly, how do I know if I hire you that you won't change your mind and leave?".
If there are gaps, let there be gaps. If they question the gaps, that's when you have to explain, not on paper. BTW - I wouldn't do a cover letter. You want a one page resume for this sort of position. Most HR in stores are going to toss anything with a cover letter. In fact, are you sure you even need a resume for this? At store level, they're not usually needed - I never used one until I applied at corporate.