Hello, @TFS,
For the cart page, you can use the static block, you have to use/set the static block widget under Appearance >> Widgets >> Cart Area as per your requirements: https://postimg.cc/HjW573Cq
OR you can edit the Cart and Checkout pages and set/choose the static blocks to show on the page from 8Theme Layout Option as per your requirements: https://postimg.cc/f3G63kFL https://postimg.cc/FdQNMPhD
Please note that these options will only works with the default layout of the cart and checkout pages not with advance cart/checkout layout.
Regards 8Themes Team.