What is the best practice to use sequential test-cases?

I know that, in test automation, we have to have avoid sequential test-cases.So, the order of running the test-cases are not important.

I believe in some cases the sequential test-cases is not avoidable:

Consider a scenario which a user needs to take some previous steps in order to complete a final goal. For example, a user needs to be logged in, so that he can purchase.

   Given User is logged in
   When  User adds an item into its basket
   And   User Complete his purchase
   Then  He receives an Email

So, in above scenario, each part (Given, When, And, and Then,) are seperate testcases. But still the order of testcase is crucial.

So, how do you write independent test-cases in end-2-end testing?