Not the one you asked about, but in Season 8 at at least four of them are sporting this exact crossbody sling bag:

https://www.ebay.com/itm/denlix-Tactical-Sling-Bag-Chest-Pack-EDC-Molle-Backpack-One-Size-Black-/153770347647

https://www.amazon.com/Tactical-Shoulder-Outdoor-Military-Backpack/dp/B07WLRJNTJ

EDIT/UPDATE: I finally found it. Holy shit that was hard to find.

It is an "Everest Messenger Bag - Medium", and it's featured by at least four contestants on Season 7. The manufacturer's website is awful. It appears the bag was slightly altered over different runs, and it's been manufactured in two sizes (Medium/Large) and all sorts of colors in the past, although the contestants all seem to have the Medium Gray variety. If you do a image search you can see the different versions:

https://duckduckgo.com/?t=ffcm&q=Everest+Messenger+Bag&iax=images&ia=images&iai=http%3A%2F%2Fwww.everestbag.com%2Fwp-content%2Fgallery%2Fbb005-bl%2Fbb005-bl.jpg

It comes/came in a Medium and a Large. The Large has more of a squarish front flap where Medium has more of a teardrop like shape for the flap. You can find a few random ones on Ebay, and the black one is here available on Amazon:

https://www.amazon.com/Everest-Messenger-Bag-Medium-Black/dp/B00158WRH0

Enjoy -