Empty bag every night of all books and as mentioned upthread, put the books into the magazine files of when they are next needed. A printed timetable next to where this takes place is essential. We also had a timetable on the back of the front door and the breakfast bar where they ate breakfast. They also had a laminated one in their pencil case too.
We had a homework time period, home, get changed, snack then homework. If no homework then time was spent expanding learning whether actual stuff they were covering in school or general learning about the world.
Whiteboard or notice board labelled with days of the week so they can write their homework on it under the day it is due in. The date it is due in was also written so they can see what to prioritise and you can see what they have.
2 pencil cases in their bag, one with the essential day to day equipment in and then another with compass, protractor, etc plus spares of any of the required equipment, for my sons that included whiteboard markers, pens in different colours, ruler, rubber, pencil sharpener, pencil. Kids can nick stuff to deliberately get you into trouble for the next lesson. None of these ever leave their bags. You have extras of these at home so they never forget a pencil case.
DCs used a locker in year 7 where they left their pe kit. As it meant two bags I made sure that their school rucksack had a carabiner clip to clip the straps of the pe kit to the main bag, that way you can't accidentally leave it under a table.
Make sure your child knows your mobile number off by heart and put it in their planner.