Cheating a bit, as I'm commuting on a tourer which I can't be bothered to strip down till it gets used again. It's a aluminium MTB and in current form comes to 18-19kg, so guessing must be fair few kilos of junk:
Front lowrider rack
Rear rack
Barbag clip mount, occationally the barbag
Computer
Large pump + luggage strap and spare bungees holding it to frame
Front lights + battery pack + couple of LED flea type back up thingies
Rackmount light + backup seatpost light
2 x mudguards
3 x bottle cages
3-4 plaggy bags jammed under the seat
Seatpost mounted cable lock
Hoseclips to lock q-releases on both wheels + seatpost clamp
Large rear pannier, containing:
Touring toolkit including neednose pliers, chainbreaker, ducttape, spare minipump, penknife, assorted spanners, allen keys, puncture kit, etc.
Headtorch
Sealskin socks, possibly a waterproof if not already using as a windstopper
Wolly hat
2-3 bungee cords
Whatever book currently reading during lunch
Work clothes
D-lock if planning on stopping someplace on the way home.