I doubt that you'll get it back. Maybe another patron got it and not the restaurant itself. If that happened don't expect to get it back. Or the restaurant people split it among themselves, that's also possible.
Consider also the cost of shipping and that reward you are offering. It might be more expensive than the items you lost.
It's Amsterdam, he'll get it back, we're talking about the Netherlands here.
Yes people are nice there, he can find someone to help him, why would someone steal his things for 100$ its almost nothing there, few grams of weed. As I understand you forgot your bag in restaurant on Prins Hendrikkade, why don`t you find their number or mail and wrote them directly, I`m sure there is at least one normal guy that works there and he will send your bag back, just find their mail address or some phone or any contact. I wish you luck my friends, I lost couple things and I know how it feels.