I always like to do as much real world math as I can throughout the year, but it's much easier to focus on it when summer vacation is looming. It's not busy work, nor is it completely unrelated to what you're teaching in any middle school math class up to Algebra I. It will keep students more engaged in a time where it's easy to disengage, and demonstrate to them clearly how many of the skills and problem solving strategies you've work on all year could actually be useful in their lives.
This activity came to me in the mail, quite literally: banks and credit card companies were sending me offers for big loans to pay off my debts (or just to spend frivolously--they couldn't seem to make up their minds in their sales pitch letters). The monthly payments always seem reasonable, until you look at how many months you'll be paying. If you do the math, you start to see just how much you're actually spending to have cash right now.
I've used newspaper ads for rent-to-own stores for similar lessons in the past, but this was different. The mailings I was getting contained concise applications that I shrunk down and copied; for the purposes of sharing without being sued, I created a sample application (complete with loan offers, payback options, and a form asking for a lot of personal info). Feel free to use it as-is, or replace the first part with an offer you receive in the mail. The document is hosted on Google Docs: