Even in this electronic age sometimes you need to leave a written message. It helps if you can make it waterproof (these notepads will help) but it is also important that when the time comes to write it that your pen works (and is ultralight, of course!) You could just use a cheap length of pencil. Or a space pen refill (as I have done here). Or you could investigate this idea – a pen which does not use ink and which does not wear out.
I have sometimes needed to leave a message – perhaps tied to a tree eg warning about some trail hazard ahead (a washed out bridge perhaps), or placed in someone’s tent/camp/hut or besides their trailcam, and of course we have all needed to fill out log books in hts etc. It is just on such occasions you find that your trusty biro which you have carried for endless trail miles has gone dry and =that no amount of rubbing an cajoling will bring it back to life.
Space pens are superior in this regard and have never failed me so far, and at one gram for the refill I carry (and little need, as I rarely venture where there are other folks to leave messages for anyway) I am unlikely to carry anything else, but if this description is not you then maybe an everlasting pen is your solution?
These pens would not actually last forever either as they wear away slowly by leaving a thin film of indelible soft metal as a message something like writing a message with the soft tip of a lead bullet something which f you are a hunter you have probably frequently done!
The one at the link below costs 19 pounds (April 2021) and doesn’t say how much it weighs. I would guess 3-4 grams. Clearly an elite product, but it might be just what you re looking for.
There are cheaper alternatives of the same basic concept however. The Amazon and eba ones are the cheapest but not necessarily the lightest.
And if you do a bit of handyman stuff as I do and are sick of sharpening wooden pencils and having them break there is an ‘everlasting’ type of carpenter’s pencil which I own a couple of and will buy more (against loss) if I see them for sale again somewhere: