I've found backpacks can be a pain to deal with and to pull lenses out of. I've got a few of them but its usually only my messenger bags that I bring to gigs if not a Pelican.
When you have a battery pack and a long lens on a camera there's few bags that it will fit in with enough cushioning and protection. The Vanguard messenger bags just fit right, and no they're not paying me to say that.
Sadly they don't make the one I bought years ago that is still perfect , but its like this one Amazon.com: Vanguard VEO GO34M BK Shoulder Bag for Mirrorless/CSC Cameras - Black : Everything Else