I have been ramp checked once in the UK at Humberside when the police, customs and excise and the CAA were there for a whole day.
They didn't actually need to see any documents there and then. They did want aircraft details and details of the pilot, licences and of the flight you had just landed from, ie departure point . I assume they checked the validity of licences, C of A etc in their own time.
For most people the time involved in the ramp check itself was no more than five minutes. Those who tried to take a high handed stand against authority somehow seemed to incur additional delays.