Last Friday I was at work, and wanted to get something out of my rucksack, so I just stuck my hand in and groped randomly rather than actually looking at what I was doing. I was quite surprised to pull my wallet out! The obvious explanation is that it had in fact been in my bag the entire time, but I'd somehow failed to notice it, even when I was explicitly looking for it. The alternate explanation is that it wasn't there until I reached in without looking at it, or for it; not quite "Schroedinger's rucksack", but something along those lines. I recall something similar from the Narnia stories - the doorways (e.g. the wardrobe) would only work when you weren't looking for them. I'm not actually accusing Mr Tumnus of pickpocketing me via an interspatial portal, but it's weird. Longtime readers may recall something similar that happened to me in my youth, when I duplicated a Skudo token.
Ah well, I got my money back, and it's prompted me to update my Sentinel records, so there's a happy ending :)