Consider switching to a APS-C type mirrorless or Micro Four Thirds. They might not be as good as a full frame DSLR, but the lenses are a lot lighter and compact

Consider switching to a APS-C type mirrorless or Micro Four Thirds. They might not be as good as a full frame DSLR, but the lenses are a lot lighter and compact. So instead of carrying around a backpack you can easily fit everything into a small messenger bag which you can easily take everywhere.