There is so much good advice that with my meagre motorbike travel experience I don't have much too add.
From my backpacking days, I used to like to keep a couple of hundred dollars under my insoles - If you lose your boots, you are in trouble, so it seems like the best place to keep some emergency cash to me.
Otherwise, all the age old advice about keeping cash in as many places on your body as possible, know where everything is at any given time, dummy wallet, exactly what all the good people have said!
On the bike, I like the back of the headlight idea, and might go with that one. Maybe behind a bar end weight? Although I'm not sure that they are meant to come off as easily as they do on my DRZ!