Do a search, I think its been covered before with good a list.
I carry: HD tool kit, multi-tool specifically for HD, spare plugs, tire plug kit, co2 tire inflator, multi-screwdriver, adjustable wrench, spare fuses, cheap multimeter, flashlight, plug gap tool, tire pressure gauge, tie wraps, misc. other small stuff, maybe more. All of it fits in small canvas tool bag in the corner of the saddlebag.
Bodeen