With a few items in your basket, the Checkout button is often pushed down below the fold, especially on mobile. This makes it less intuitive and slower for users to checkout.
One option is to have two Checkout buttons in your basket, one at the top of the page and one towards the bottom, underneath the list of products.
Another way is to have an Order Summary panel in the basket (this can be sticky in the right hand column on desktop), with the Checkout button as part of it. This option ensures that the Checkout button is always on screen for desktop devices at least.
Salesforce data gathered from across clients on their Commerce Cloud platform showed that conversion improved 3.5% where the Checkout button was always on screen in the basket.