Help your child become organised for success!
Ideally, what should happen is that it is put consistently in the same place. As a matter of routine, the youngster unpacks it. Sportswear that needs washing is put in a laundry basket or in the washing machine. Any sandwich box needs to be removed and washed, ready to put fresh sandwiches in for the next day.
There also needs to be a routine for packing the bag for the next school day. Youngsters can identify what they need from their timetable and planner.
Then there is the question of storage. There does need to be somewhere where things for school can be stored. Box or shelf, it needs to be in plain view. Under the bed is not a great option, as out of sight can be out of mind. It needs to be routine that school things go in the storage box, or on the storage shelf.

It makes sense to have a copy of the timetable, where it can easily be accessed.
What items does the youngster need for school? Does he or she have spare pens and pencils? Who replaces them when they run out or get lost? Where are glue sticks, scissors, etc, stored at home? Well, again, these are questions that may not occur to the youngster, until the last minute before he or she needs them. It is worth parents discussing with their child what sort of things are needed for school.
There may be things that the whole family shares, such as a hole-punch or pairs of scissors. It makes sense that these are stored in the same place each time after use.
Once an exercise book is filled up, it may not necessarily be finished with. It may be needed for revision, or it may contain a coursework draft that may be useful if coursework is lost. It needs to be stored at home with the school things until it is certain it will not be needed.
Once a topic has been finished, then it makes sense to store any paper related to that topic at home, rather than carry it around. It avoids the situation whereby, if the schoolbag or file is lost, the whole of the work is lost. The papers need to be put into a storage file.
Once the school things are organised, the next step is planning.