I have kept a journal on-and-off for a number of years. I keep notes for the purpose of becoming a better hunter and for my younger family members (I would like to think that they may like to read them in order to become better hunters).
I believe it's a very good idea to keep track of the following information. It does not take long, but over the years, assuming you hunt the same area year after year or at lest every so often, it will make a difference in the long run to your hunting success.
1. weather ? temp, humidity, wind and direction, precipitation, ground cover ? how much snow or rain fell/is on the ground etc.
2. previous weather and when it started (if you know) I like to watch the weather in my hunting area and note the first real snow fall and the first real long cold snap.
3. time and light (can you see and when can you see)
4. how long it takes to move around your hunting area
5. how many and the sex of the game you see
6. type of deer ? WT, Mule, Elk. . .
7. how long it takes to get to a particular location
8. best routs or directions to move around in an area
9. secret deer hideouts or special areas that I do not want to forget ? crossings or holes
10. where I kill deer ? if I kill deer. . .
11. what the deer were eating and how they were moving
12. map their movements if possible
13. if I found water or need to take along gear that I did not bring
14. other ? anything special or out of the ordinary like other hunting pressure, cats, bears, and what the deer do.
15. Topography and elevation ? where are you seeing the deer.
Later, you can match the variables together from years of information and get a real good idea of what to expect and how to better hunt your area.
In the final analysis, I jot down everything that comes to my mind that may make my hunt more successful in the future. You can not write too much! Weather, timing, deer activity are the most important to me. You would be surprised at how easy it is to forget how long it took to get to a location. Weather plays a big part in timing so I write it down so that I know how long in might take to get back to a specific site. If you hunt a long of different areas or do a lot of hiking, you will soon confuse one area with another ? I also write down how long it takes to drive to a spot. Again, the weather can be a huge factor in this so I take notes so that later I know how much time to give myself to get to a specific spot.
I guess I would like to think that someday my nephews will pick up my journals and use them to hunt the same areas. I know it would be nice to have 20 years of notes on a a particular area written by a guy chasing deer.
I almost never write in the field unless I'm camped out and have not choice in which case I will take a small note pad and PENCIL, never a pen! Pens fail, freeze, leak, run if the pad gets wet etc.!
Take care, good luck.