def METHOD_NAME(self, instance):
    content_bits = []
    for field in doc_fields:
        file = getattr(instance, field)
        if file:
            content_bits.append(file.title)
    for link in instance.activity_documents.all():
        content_bits.append(link.documents.title)
    for link in instance.handout_documents.all():
        content_bits.append(link.documents.title)
    return " ".join(content_bits)