Things needed to perform an activity - requisite or requirement? Or something else?

Solution 1:

Let us consider these two words in their noun forms:

The university has an entry requirement.

Requirement, as defined by Collins's Dictionary, is something imposed or demanded as an obligation. Therefore, requirement, by definition, has a degree of arbitrariness. Here, the university decides to arbitrarily impose this on students.

No matter how hard they try, they simply do not possess the requisite skills to do the job.

Requisite is something indispensable or necessary for some purpose. It implies that something is essential or vital. In this case, the persons trying cannot be hired because they lack the skills, which are absolutely necessary for the job.

Now I hope that this has clarified the meaning for you. But whether requisite or requirement is correct depends absolutely on the context of your sentence. Perhaps you could give us a precise one?