Hi Scatterbrain
Off the top of my head... microfiber cloth, lemon oil, string winder, clip-on tuner (not really a toolkit thing I suppose), spare tuner batteries, spare strings, something to cut strings with (I like to use heavy duty nail scissors), spare nut and saddle blanks, files, sandpaper, masking tape, wood glue, soft toothbrush, steel ruler, other stuff I can't remember...
I have no special preferences although I do like the fact that the Jim Dunlop lemon oil comes in a spray bottle
Oh, and a pencil case to keep most of the stuff in... and a pencil (for lubricating nut slots)...