It may be interesting to observe that people who are renting are having to carry a huge amount of stuff. For example pencils and a pencil sharpener (incidentally why not use clutch pencils, notwithstanding them not being CAA approved?)
If you have your own plane, or are a member of even a half civilised syndicate, all this stuff can live in the plane full-time. That includes all the required aircraft documents.
Then all you need to worry about is your personal stuff: passport, pilot license, medical, radio license if flying an N-reg, etc.
Then there is a long list of specific stuff like shaver, toothbrush, spare mobile phone, a spare set of aircraft keys for a passenger to carry... well you get the idea. I have a long checklist of things to do pre-flight (routepacks, printing out approach plates, weather, notams, PPR, etc) and on it is a long list of things to pack. I can't post it because for some reason I can't find the original document...
Incidentally a list, believed to be accurate, for N-regs is
here.