Any purchase I make, the shop needs my address and my payment info. It's always the same. Every browser can autofill it, if they bothered using the correct forms. Once the transaction is done, the invoice mailed and the product shipped - there is 0 need for this data to still be stored in their database.
-> Address and payment info - browser auto fill
-> purchase history - invoice via mail
I used to be heavily biased to buy from Amazon, since it is basically one click. But lately, I'm more and more buying from smaller online shops which provide checkout without user account.
I'm sure there is many things where you need to store user data, but also, there is definitely more things were user data is stored although it is not needed.
And ultimately, that is the spirit of GDPR - ask yourself if you really need to store that data.