I use Ocado for my groceries. By default they will deliver based on a combination of things I've marked as "every X unit of time" and a predicted/suggested set based on past purchases. Then I can log in before a deadline to amend it. 90% of the basket typically remains unchanged, and quite regularly I can't be bothered to even log in to check what it's selected for me because I know it'll be close enough unless there's something specific I absolutely need this week.

No reason why Amazon can't do something similar. They only need it to be "good enough" that people start getting used to not always needing to ask for it to list what is in the upcoming order.