[yawaramin]

> With a cart you might want to add a ‘cart state/session’ id so you can share it

That might not work for carts that work by temporarily 'booking' an item, like a seat for a cinema ticket. By definition, the cart is unique to a user.

[graftak]

My local cinema actually allows this but the cart-session is tied to the user session so when you share it the page goes to readonly mode where only the time and chosen seats are visible.