I'm out of votes for the day, but if I could, I would ++hippo for each of the following items from that checklist which were part of my troubleshooting steps:

1, 3, 4, 7, 10

I would further point out that things I had either intended to do, or would have done with my own work, include:

1, 2, 3, 4, 5, 6, 7, 9, 10

The only item missing is #8, and I don't use those merely out of habit -- but I do ensure every handle is unique globally, which is a less foolproof system, but due to my own rigorous adherence to my own standards, has never failed me in a few decades of using Perl. :-)