My camera bag is actually a pacsafe travelsafe 12 litre, house in a samsonite 26 litre trolley laptop backpack. Bag weight 2kg in total, offer protection against theft and trolley bag is a saver for my aching shoulder.
Len are kept in separate pouch, in travelsafe 12l to prevent abrasion when pack together. I manage to load in .. 2 D600, 2 SB900, 14-24, 24-70, 70-200, 28, 50, 85 (basically all the equipment I cant afford to lose)
Camera battery, laptop charger, laptop, video cables, umbrella, sirus tripod, LED light, blower, snack etc in the samsonite.
This setup is for wedding shoot, for walkaround shoot I just load in one camera and 3 len.