Not in any particular order and not what I advise to pack - more what I have accumulated from several trips and now always seems to be on the bike or on my person:
Credit Card + a bit of cash (never leave home without it anyway cash is good if you struggle to get fuel at a self service station...)
Breakdown cover (Europe wide)
Phone
(Tools or parts)
Spare bulbs
Small bottle of super glue (I have used glue twice now, 1. to glue a tab on the back of my sat nav to keep it water tight 2. to glue a split seam on my boots to make them do until i got home on a 2 week trip)
Puncture bungs (already have glue on them and look like a "cat turd" but saves fecking about with glue compound....- search the internet...)
Puncture kit bradall
Miniature Air compressor (I have a lead that plugs to the Optimate lead that is constantly fitted to my battery - note: always run bike when running compressor...) - I have used this 3 times in the last 4 years and never for myself always to help others sat at the side of the road....
Small tool kit comprising of:
Multi tool with pliers and a good knife (this gets used every day anyway for opening cans or cutting bread etc)
Small T bar with socket and interchangeable bits to fit: rear wheel bolts / front pinch bolts / body panels (these are mainly for tightening anything that comes loose rather than removal...)
Flat and Pozi drive screwdriver (interchangeable shank) from BMW tool kit.
Couple of cable ties - which I have never used but take up feck all room.
All of the above fits into an adventure warehouse locking tool kit that is bolted to the inner side of my offside pannier rack they're always on the bike and have toured most of Europe with me and seem to do the trick.
I look at it this way - I can buy oil from a garage (but I have carried oil in the past but now don't see the point) - I have stopped a few times to help other bikers that have had a problem (3 punctures and 1 electrical problem) each time we got them all going and on their way). I am sure if I carried less there would be someone along within and hour or so that did carry a tool or part I needed but in real terms I havent taken up any "luggage space" with the few items I have.
Rik