Last year I forgot my water bottle on my commute in to work. I rarely drink on my commute in: I leave before 6 am, and it's only about 15 miles, so I only occasionally feel the need to drink, but that day I reached down to get my bottle and it wasn't there. Fortunately I keep a spare (empty) bottle in my desk drawer (in the summer, the temps on the ride home can be well over 100 deg F).
Oh, and like grampa, I once drove about 50 miles to the start of an organized ride only to find I'd left my shoes at home. No fun riding a tandem with Speedplays in tennis shoes.