Handgun is my bread & butter so some info that is helpful for rifle is superfluous for handgun. I keep date, rounds loaded, bullet brand, weight, style, powder, charge weight, COAL, primer (if it is a primer OTHER than CCI non-mag) and I denote head stamp.
That's all I keep for handloading...
But my log is simply dated entries and it reads like a GIGUNDO diary of all my handloading, shooting, range trips, gun acquisitions (and the few that go away also) and I also log the price I have paid for many of my different purchases (bullets, primers, etc) so I can compare trends in prices. Sometimes I will see a price and think "Hey, that looks like a good price!" and I will check the log to see what I paid for it a year back and sometimes I adjust my thinking.
The part of my log I like the best is that I now keep very strict round counts on all of my guns. It does annoy me that guns I buy used (pretty much all I buy these days...) typically don't come to me with a round count, but it annoys me even more than some of my own guns that I got new (before I opened the log!) don't have an accurate round count. Either way, I find it very fun and very interesting -- in very much the same way a motorcyclist looks at his ever-rising odometer as a badge of honor, I do the same with round counts.
Keeping round counts is also one heckuva fine tool for trouble-shooting certain issues. When I have had to fix or tweak an extractor or do some work on a disconnector, my round counts let me know exactly how many flawless rounds I have had since the "fix" which helps me determine which guns are
FIXED and which guns are still in the process of being vetted.
The handloading log is as important to me as my press, it helps me duplicate my BEST loads and it also helps me to avoid accidentally repeating loads that weren't very good. But my log of round counts is the part I like best.
I know many folks roll their eyes or their head wants to explode when they even consider the idea, thinking it must be a monotonous pile of work, but it's all in what you make of it. To me it is just another "collecting" kind of hobby, it's just that it is raw data that I am collecting.
My EDC has 6,452 rounds through it.
Not that anyone wondered.