Sold Galleries allows you to have a page dedicated to your past-sold products. If enabled, sold out products will be moved here instead. First, navigate to Design > Navigation. Under Link Labels, give "Sold" the name of your choice.
Next, navigate to Store > Settings. Under General Settings in the When sold out section choose "Move to sold section". You can also hide prices on sold out items. This is a good idea for products that may be gifts.
Now your sold out products will be in the sold gallery! By default, it is added to the top of your list of pages. Like any other page, you can change the order in Content > Pages.