This is the most effective way to pack a rucksack.

During the day, food and spare clothing is easily accessible, whilst essential kit to keep dry is protected inside the bag

When arriving in camp, and if bad weather, shelther and food can be easily accessed from the base compartment - without getting everything out. 

The last thing needed is the sleeping bag and dry clothes

Rucksacks are not waterproofs, rain covers are not 100% effective. Kit should be appropriatetly protected, ideally using dry bags, but rubble sacks will work.

Camping  mats attached to the outside of the bag should be waterproofed - if it rains and they are soaked through this is going to make participants sleeping bags wet.