For younger children, I liked to keep a brightly coloured vinyl envelope in the backpack for notes, permission slips, lunch orders....anything that needed to be sent to school or from school to home. Fewer papers got forgotten or lost in the bottom of the backpack. The bright colour was a good visual reminder. Paperwork was safer in the vinyl, protected from lunchbox leaks or rain or other potential injury.
This is the sort of envelope I used, but you only need 1 per child, not a pack of 15.
Possibly most of this paperwork is handled on-line these days, but if you anticipate communication flowing back and forth to school, this adds a little organization and security.