The Angelic Host is going to war. It's a long journey, requiring flight over the highest mountain ranges and long trudges through the fiercest blizzards.
As with all large scale military marches the Host will be carrying equipment, tents and provisions for the journey and the eventual battle, averaging 30kg of gear per angel. Each angel is the same physically as a well built human, but with a pair of large birdlike wings based just behind the shoulder blades that enable them to fly by pushing off Plot particles floating in the aether (you can assume these wings are strong enough to deal with the extra weight).
Naturally hands need to be kept free for wielding flaming swords and throwing thunderous spears and playing mighty trumpets etc, so how might an angel keep all their equipment about themselves without interfering with their wings (or ruining their backs)?
EDIT FOR CLARITY: I don't care about the equipment in the knapsack, I care about the manner of attachment/storage. The question can be most succinctly written as: 'How could my winged humanoids attach items/goods to their bodies in such a manner that they can keep their hands free, fly and walk'.