Yes, I usually remember to pack an extra pair of glasses but often I forget. I never stop to think what a disaster it would be to lose them on a trip, especially a special trip to someplace with a lot of sights I had never seen.
I have forgotten camera battery chargers (no fun) so I couldn't take pictures.
Many years ago we were just about to hop into a taxi in NYC to go to the airport to fly to Europe when I realized I had left my passport downtown. I had to do a VERY quick subway dash to go get it. I think I was able to make it roundtrip in about 55 minutes, fortunately we were in the habit of leaving very early for international flights.
I had to get on the A-train at 72/Broadway and change in Times Square to the N and go to 8th st. - run to my apartment and get my passport and do the whole riude in reverse.
The thing about subways is that you never know how long a train will take - you may catch one, or just miss it (which can mean a 20 minute wait).
Why didnt I take a taxi - because they not only cost more, but if traffic is bad they can take longer.