Inspired by the unfortunate circumstance of @noglider and my recollection of a similar incident. Let's say your bike was locked up and someone took your stuff. Or, you left your bag on a bench and it was not there when you came back. What would you replace the contents with? Is there anything you really like that you can't replace? Is there anything you would like to try? Do you have a souvenir or totem in there you would miss?

Let's keep it to gadgets (tools, lights, etc) and specifically avoid bikes, locks, and clothes - exception for anything you normally keep packed up, like a poncho. I think also excepting the bag itself since that'd be a recent retread thread.

I had a Topeak Power 21 multi tool that I really, really liked. It no longer exists for retail. They do crop up on ebay.

I like my headlight pretty well, and the Hong Kong company that sold it is still going, but it looks like the specific model is gone. It's part of the whole flashlight nerd hobby and that particular diode was just finished in that market. In order to replace it I'd need to... study! yuck

I have a Mountain Morph pump and though it pumps great, honestly it's too big for most bags and I feel it would rattle off the frame. I'd get a smaller one. Maybe now an electric one.