If I go to an e-commerce website and I am not signed in to, add a bunch of stuff to my cart and leave, I have absolutely no expectation the cart will persist until the next day, and I really don’t think you should either. Not only is it in an unreasonable expectation as an end user, but also it sounds like an absolute nightmare for businesses (Do you hold physical inventory for things in the cart? What about price changes or products are discontinued? Etc).
In practice, sellers do deal with this. The most common approach is that putting something in the cart does not reserve it or maintain a fixed price. Then if availability or pricing changes, they flag that to the user when viewing the cart.
