Simply log back into the site and your shopping cart will restore itself. The site has a session timeout feature in case you step away for too long.
Please note also that the items are available to purchase for everyone until payment is completed.
What does this mean and why do we do it?
As an example, Jack and Jill are both shopping on the website and they both have the same product in their shopping cart which also happens to be the last one.
If Jack decides to continue browsing and Jill completes her payment, then Jill will get the product.
Why do we do it?
Over the years we've had "bulk buyers" browse our website and put 1000's of products into their shopping cart which we thought was just totally unfair so we removed the basket reservations option so everyone got to enjoy the products. Fair and Square
Note to self: It's very rare when this happens, but just bear this in mind