If by logic or practical reasoning you can tell which action happened first, you do not need to worry about using the past perfect. The same is true when a conjunction makes it clear which event happened first.
Consider the following:
I opened my door and stumbled down the steps.
After I ordered my meal, I went to wash my hands.
At the time (that/which) I lost my job, I started looking for another one.
In all the above, no past perfect is necessary to determine or declare which event happened first, and the same is true of your sentence:
When Sally received her first pay, she bought presents for her parents.
When here means at the time (which). It can even have the force of after. We know which event happened first by common sense and by the appropriate use of conjunctions.