I see certain regulars at the local coffee shop and many of them carry their notebooks (whether or not it's a MacBook is irrelevant) to the restroom.
Another way to do this would be to put the device in a backpack, secure that to a piece of furniture. I typically walk around with a generic-looking black daypack with a multitude of zippers. I have a small padlock to lock most of these backpack zippers up. Granted, it's pretty easy to bust through a nylon zipper, but it's not something most would try in a crowded public area like a coffee shop.
Myself, I own an 11" MacBook Air (mid-2013) without any sort of lock port. It replaces a MacBook (late 2006) that had the Kensington lock port. Guess what? I think I've used the lock port maybe 3-4 times (I still have the infernal lock).
Apple was pretty much right in ditching the lock port.
Take the damned Air into the the restroom or have a neighbor look after your stuff for a few minutes.
Not a big deal.