WB, good of you to be so magnanimous to your successors - an unusual quality as any sysdamin would tell you!!
You need to put the following into a script (say cancellall.sh) using vi or another editor of your choice:
while read queue
do
cancel $queue
done < list.txt
and create your list.txt with the names of the queues, each on a separate line and exactly as they are if using the cancel separately.
Make cancellall.sh executable (chmod 755 cancellall.sh for example) and run it using ./cancellall.sh from the command line.
If you wish to run it nightly as originally stipulated, you'll need to set up a cron job in the format (example):
00 03 * * * /path/to/cancellall.sh
to run the script at 3:00 am every day.
Hope this helps.