If coming from W.A., a copy of rego papers since we don't have rego disks over here.
Not a good idea to keep them with the bike especially if it gets stolen. Plus police nation wide know your rego details from the plate number before they stop you.
What I can up with is "generally it's something you haven't needed on previous trips and you leave it home""
But
loo paper or
baby wipes (better) come to mind.....Sorry girls but there times when you simply have to go and the nearest loo is 50 kms away.
Insect repellent........though the last time I used it the flies weren't told that it was supposed to repel them instead of nearly carrying me away.
Hair Brush........There's one in the bike at all times so Heather can do her hair after taking helmet off.
Pens.........I keep one in the bike for mileage details on fuel docket.
Cig lighter/matches......if you need a camp fire.