I’m not on a pump and don’t have a CGM, so I keep all my records on a spreadsheet. I’m retired, so most of my readings are taken at home. I keep my testing equipment on my computer desk and my insulin handy, so it is easy to record everything on the spreadsheet. Of course, on those days I take BG readings while I’m out, I just transfer the records from the memory on my meter to the spreadsheet when I get home.
And yes, in addition to columns for date, time, fasting BG, other BG, and insulin doses and type, I have a wide column for notes. Among the things I note are when I start a new Lantus or Apidra pen, how much my BG dropped over a certain period of time (on occasions when it seemed unusually fast or slow), and what I might have had to eat with a certain meal. This allows me to go back later and do a search for certain things. Like I might wonder how many units of insulin I took with a certain Chinese take-out meal and whether it was the correct amount. The next time I order that meal, I can look it up and adjust accordingly. I don’t bother listing food with every meal on this form, just those I expect to need as a reference later.