Everlane* probably can’t endorse this particular use of their backpack, but it is making Watson adventures possible!
Some notes on safety: As happy as I am about figuring out new ways to explore the city with Watson, I would not recommend this unless your best friend is an odd velcro dog without any escape instincts. Watson was secure and safe inside the bag, but only because he had no interest in getting out. In one test run at home, I put the backpack down, drawstring loosened, on the bed. Watson looked around, shifted to a more comfortable position, and fell asleep, still inside the backpack. While waiting for the train, I wore the backpack against my chest, where I could wrap my arms around him. Additionally, he is wearing a collar and leash; the leash is tied to the strap of the backpack.
* If you decide to use this link, I get credit — thank you!