The other day, I put my Jetpack and Nano Boots in MFEs to charge them. While waiting for them to charge, I decided to go out and jump into my quarry to see if it had uncovered any nice XP-giving ores for me to dig manually. After all, it had dug all the way down to layer 15 or so, so there should be plenty of fun stuff down there.
My base, where I had left my boots and jetpack, is located at layer 75. Which means I had plenty of time to think "wait a second..." while in midair.
Same here only I did it in the End. My brother and I had setup a mystcraft portal location off the main landmass, We returned to bass to arm up to take the dragon so I dropped off my nano suit and jet pack to top off to full. I arm up to tackle the dragon portal, portal through to the end and then jump off the floating island to find that I had grabbed my armor and jetpack but had forgotten to put them on...