Bluskis, yes I keep the documentation relating to the a/c in it, my own stuff (licence etc) I keep in my bag which I do keep with me whenever I leave the aircraft. Part of the reason for this is that I like to empty out my pockets before flight so I also need my bag with me for money, phone etc.
Your experience obviously emphasises to us all the usefulness of carrying additional documents at an "unfamiliar" airport as of course you did.
Why they then fussed over your licence and medical in that way God only knows???
At Perpignan I only had to show my licence and passport to return airside (which I had with me). Menorca wanted to see the aircraft docs (usual, apparently on first visit there). They passed a message via the pickup bus to bring these so I simply collected them from the plane before leaving.
It is an anomaly that the fuel company doesn't take credit card (yet "Aena" do, for the other charges). To be fair I had been warned prior to the visit that I needed cash for fuel so had taken plenty ('least EUR can be used in most of Europe).
Fujiflyer