Amazon offers a selection of kids' backpacks, with prices starting from $5.92. Plus, Prime members receive free shipping. (Non-members can spend $49 to qualify for free shipping; otherwise, shipping starts at around $5.) A couple of best bets:

• Disney Boys' Miles From Tomorrowland 12" Backpack for $9.12 (low by $9)
• Despicable Me Boys' Student Of The Month Backpack for $10.08 (pictured, low by $4)