The infamous "Front Seat Hidey Hole"! Been there and done that.
Wife and I came back from a camping trip to NC one last year and I couldnt' find my Mountainsmith fanny pack. It's a long-time favorite piece of gear and had a $150 Surefire flashlight, a Princeton Tec headlamp and some other first-aid and misc gear.
Looked everywhere for it, called everyone and was just Sick about losing it!
I think it was 6 or 7 months later my wife comes up to the front door and says "How much do you love me? I got something for you!" The darn thing had gotten crammed up under the seat of her Honda Odyssey and she found it while cleaning the van! It had to be hidden pretty good too because she had taken the van to be cleaned a the local car wash 4 or 5 times during that time period and they never found it either!
I looked for it for over half a year and had been sitting over it at least once a week that entire time!
Glad to hear that everyone got their stuff back!