A favourite exam question is "which of these must be carried on the flight?", so learn the list and, just as important, the exceptions that let you leave it behind. The full set of documents to be carried on each flight (Part-NCO.GEN.135) is:
the Flight Manual (or equivalent);
the original Certificate of Registration;
the original Certificate of Airworthiness;
the Noise Certificate (if applicable);
the list of specific approvals (if applicable);
the Aircraft Radio Licence;
the Insurance Certificate;
the Journey Log;
details of the filed flight plan (if applicable);
current aeronautical charts for the route and likely diversions;
the interception procedures and visual signals information;
the Minimum Equipment List (if applicable);
any other documentation pertinent to the flight.
Now the exceptions, which are where the marks are:
On a flight taking off and landing at the same aerodrome, items 2–8 may be left at the aerodrome.
For a non-Part-21 aircraft flown within the UK, the only carriage requirement is charts for navigation.
For a flight entirely within the UK, Channel Islands and Isle of Man, no documents need be carried at all.
When exercising the privileges of a Part-FCL licence you must carry the licence and photographic identity (driving licence or passport).
On a private flight involving international air navigation, only the first five documents (items 1–5 above) need be carried.
Finally, production: on request by an authorised person you must produce the documents within a reasonable time, and your licence and logbook for up to two years after the last entry.