The checkout page has a section where you can display products of your choice to entice users to buy more items. The section is titled "You might also like," as shown in the screenshot below.

The suggested products displayed will be the same for all customers, regardless of what they have in their cart. You'll need to manually add and update the products; currently there's no way to automate what shows based on data such as best selling items or related items.

The maximum number of products that will display in the suggested items area on checkout is 16. We'd recommend untagging old suggested items as you add new ones, to make it easier to manage the items and tagging. This may also reduce the chance of slowing the checkout page load times.

Only "in stock" items will be displayed, so if you tag a product which is not in stock, or if all the available qty is purchased by customers, those products will not show in the suggested items display on checkout.

Go into your admin > Inventory > Products

Do a search for the item(s) you want to feature on the checkout page

Add the product tag "checkout suggestion" to each item

Go into your admin > Inventory > Products

Enter "checkout suggestion" in the field labeled "tagged with" and then click "Search"

To remove a product, click edit, remove the tag, and save the changes

You may want to set a recurring calendar event to remind yourself to periodically update the suggested products, so they stay current and relevant.

You may want to display suggested products from a variety of categories, to appeal to customers who are purchasing from different categories.

As recommended earlier, you should untag old suggested items so that the number you have tagged is around the limit of 16. Any beyond 16 will not be shown and may use up unnecessary page load resources. Additionally, this will make it easier for you to manage the suggested items and tagging.