Along with water & air temps, depth & time and other stuff, I have always recorded how much weight I wore which has been a great help to me...unfortunately I don't dive often enough to remember how much I need. I haven't always recorded air consumption but think I will start doing that, so I can see how that varies with conditions and as I get more experienced (I'm a novice).
On one dive last fall I recorded all the junk my buddy & I pulled out of a lake popular with swimmers...makes for an amusing read. My buddy picked up a snorkel, a mask, several golf balls, a broken fishing rod with a very nice reel, a golf disc (you know, for frisbee golf), three oars, and several other things...what wasn't jammed in her goody bag she carried in her hands - was great buouancy practice! Especially since the bottom was very silty. She was leading so she got the good loot. We're going back again this fall & I'll make another list so we can compare.