The back-to-school shopping season is upon us, and retailers’ e-commerce sites should be prepared for a shopping frenzy. eMarketer forecasts that this year's back-to-school sales will total $828.81 billion, a 2.6 percent increase over 2015. Furthermore, the e-commerce portion of back-to-school sales will continue to grow, jumping 15.3 percent this year to $65.42 billion. That…