The stray isn't in there and since people have to spend alot of time clicking that add to cart thing in the game to get the catsacks, i think this Would be a Neat idea!
It was intentionally not included as The Stray is a hidden store.
To be honest i wouldn't exactly call it hidden anymore as it's pretty hard to miss and appears all the time now rather than just at night. Unless it starts moving around again like the Wandering Merchant did, i don't see why it shouldn't be added.
We have other plans for The Stray that adding it to Tower Express would work against.
Maybe after a player interacts/purchases from a store it will appear on their Express?