How to attach a backpack to a bicycle

Today I am sharing a tip on how to strap a backpack to a bicycle with a rear luggage carrier. In order to secure the backpack to my bicycle I am using the following materials:

1 x 50mm side-release buckle
2 x 50mm tri-glide buckles
2 x 50mm straps 60cm long (each)
2 x 25mm tri-glide buckles
1 x 25mm strap 200cm long

Before strapping the backpack 3 things need to be taken in consideration:

1 – Is there anything in the backpack that may might be damaged by the straps or the luggage carrier?
2 – Is the weight of the backpack within the weight carrying limits of the luggage carrier?
3 – How to keep the backpack clean?

In my case the answers to these questions are no, yes and luckily this backpack comes with its own rain cover, which I am using to cover the back side of the backpack, and that way only the front side is exposed.