*packing for a school-hosted graduation celebration with friends*
let's see, first rule of packing for a trip, count on every slim chance happening...

List of things now in backpack:
3 changes of clothes (1-night trip for an all night party in <100-MILE-AWAY MAJOR CITY>)
Laptop
3DS
3x 4-port USB Hubs
10-port power strip (not fully in bag, but mostly so.)
Extra pair of shoes
3.5" external floppy drive
First aid kit
SAK
precision driver set
soldering set
multitool
pliers (1x farmer's, 1x bent needlenose)
multimeter
empty laptop HDD (250GB)
magnet in Altoids tin (can't have it trashing the HDD!)
VGA to RGB (Composite ends) adapter
Composite/S-VIDEO USB capture card
Portable USB chargers (1x 30k mAh 2-port, 1x superslim 3k mAh 1-port)
Enough phone chargers to replace all chargers within 30 miles
Smelling salts
2x 16GB thumbdrives
Boot disc set
$200
School IDs (for bag's ID slot)
3 pairs of decent earbuds (no el cheapo $1 ones because they break trying to get them out of the package)
Serial to USB adapter
Rehydration salts
Magnesium fire striker
Plenty of pens and pencils
Emergency radio locator beacon
Emergency cellular locator beacon
SD/eMMC/CF/TF/MCP(D) USB reader
external HDD reader (2.5" IDE/3.5" IDE/SATA, external power)

am i missing anything?

Back in 2005, I had quite a few bits of music I was working on (just as a hobby). A lot of these had not been finished, but I'd sent excerpts in medium-quality MP3 format to a friend. I had an external backup drive - a regular hard drive in an USB enclosure. After a while, this drive started making unpleasant whining sounds so I sent it off for replacement.

During that time I made the foolish decision to try and plug a floppy drive in while the PC was powered on. Something touched the bottom of the hard drive and the power went off. I powered it back on again and heard a fizzing sound, there were some flashes from the hard drive and a burning smell. Yep, the disk was dead - and my backup drive was gone.

I'm still not entirely sure what happened, my best guess is that I had an exposed piece of wire from one of my hacky case mods (I had a thing for blue LEDs) which touched the circuitry of the hard drive. Almost every project, piece of software I'd created, every photo I'd taken, and most unfinished music I'd made up until that point - gone. I was pretty devastated about it. I only had a handful of things survived which I'd burned onto CD previously.

I managed to get some excerpts back from my friend, and re-created my favourite pieces of music based on those. I've moved on to other projects and write much better code now, so mostly I am no longer bothered. I do wish I could re-listen to some of the music I had made back then though.

Needless to say, I no longer fiddle around with the innards of my computers while they are on, store everything on mirrored drives and also ensure I always have a backup somewhere (and am working on remote backups and having several days of backups...)

I never want that to happen again

Finding 2x external USB (!) Floppy drives in the trash.. there were still customer data on the floppies inside it. Was a great day. Still have one :)