To auto-fill credit card information, the information must be stored as a credit card item, and the option Show cards on Tab page must be enabled. With this configuration, the autofill workflow is to open the browser extension and then click on the card item.
There is unfortunately no keyboard shortcut for autofilling of credit cards, which is why I proposed a Feature Request for Credit card autofill using hotkey or on page load last year — a vote would be appreciated.
I just noticed that on the Tab page of the browser extension (where the credit card items are shown), the credit cards appear to be sorted alphabetically. Thus, a potential workaround for you would be to prepend the credit card names with a prefix such as 01, 02, 03, etc., or to prefix the infrequently used ones with a z or zzz, etc. Of course, this won’t help if you also want easy access to Identity items for autofilling (as Indentity items are displayed below the Card items on the Tab page).