Automount USB flash disk (fw 4.0.0 +).

Example script:

#!/bin/sh
#
LAST=0
i=0
while true
do
flsh=`cat /proc/diskstats |awk '/8\x20\x20\x20\x20\x20\x20\x201/ {print $3}'`
if [ $flsh ]; then
  i=1
else
  i=0
fi
if [ $LAST != $i ]; then
  LAST=$i
  if [ $i = 1 ]; then
    echo "Mount flash disk."
      if [ -d /mnt/flash ]; then
        mount /dev/$flsh /mnt/flash
      else
        mkdir /mnt/flash
        mount /dev/$flsh /mnt/flash
      fi
  else
    echo "UMOUNT flash disk."
    umount /mnt/flash
    rmdir /mnt/flash
  fi
fi
sleep 2
done

Create a file automount.sh and copy it e.g. to root folder and start it from Startup script as you can see below.

Startup Script:

#!/bin/sh
#
# This script will be executed *after* all the other init scripts.
# You can put your own initialization stuff in here.

sh /root/automount.sh &

After reboot the router you can see folder /mnt/flash after inserted USB flash disk.