The main GCP activities are defined in the regulations: IRB, Informed Consent, Test Article Control, Protocol Adherence, Adverse Events, Records, Reports, and Financial Disclosure. An SOP that just restates the regulations is usually not helpful – you can just as easily train on the regulations as on the SOP. Similarly, for a given study, the required activities are defined in the protocol and associated documents, so writing an SOP to restate study-specific activities is redundant.
However, you might want an SOP to address your site’s specific “how-to’s,” like the use of checklists and logs, training (general, GCP, and study-specific), or internal paper and electronic systems.