$ave Me: Making the grade for back-to-school purchases

Back to school is just around the corner. Are you ready?

Parents are expected to spend less on school supplies for their kids this year, according to the National Retail Federation. But it's still a potential budget-buster. The average family will spend $634.78 on necessities for grade-school children, and $836.83 on college-bound students.

Before you head out to the stores, check to see what supplies can be reused or repurposed from last year. (That smart behavior is a big reason why families are spending less, according to the NRF.)

For a few purchases, it may even be better to skip the store altogether. College students can cut 50 percent or better off their textbook bills by renting from their college store or online vendors such as Amazon.com or Chegg. Review the policies, though, to make sure you won't be hit with damage fees for highlighting or a late charge if you need the text an extra week for finals.

By CNBC.com's Kelli B. Grant. Follow her on Twitter @KelliGrant.