You can make a list of products you would like to buy, while you think about whether to pre-order them or not, and then register the list later on.
There are "Add to Wish List" buttons on each of the product pages. Simply push a button to register the product on your list.
Please note that even if you have registered products on your Wish List, they won't be in your cart yet.
To move each product into your cart, press its "Put in Cart" button.