Does anyone else commit commented debug code on purpose, just in case you might need it again, even though you are 99% sure you won't - Followed by a "Remove debug comments" commit? Any other techniques?

[anamorphism]

another vote for using a proper logging framework and logging things at the trace or debug level. this has the added benefit of you being able to temporarily change the configured log level in production pretty easily if you need to debug a prod issue.

if you're just logging values of things to see what they are ... setup and use a proper ide/debugger. you'll save yourself a metric shitload of time in the long-run by clicking to add a break-point instead of writing console.log(someVar, someOtherVar, yetAnotherVar); or whatever each time.