I carry a small waterproof hiking booklet in my range box. Within I put notes on spine, brace, bow anatomy, info on my bows such as string length, etc. Basically anything that i may find useful when I am making archery gear and need to purchase items or remember but cannot remember 'exactly' what I should.gather my own sap, keeping my eyes open for resinous trees on college campuses usually. You're looking for the hardened globs that ooze out where limbs have been cut/broken off or the bark damaged (fresh sap is too sticky!)
I've found the ideal mixture is about 70% resin/sap, ~25% finely powdered charcoal, and ~5% beeswax. (When I first tried making it, I used about 50:50 sap:charcoal, and it was much too brittle) It is possible to over-cook it (makes it brittle), so you really only need as much heat as will make it fully sticky and workable.
I also have a camping-foods booklet with notes that range from what a tsp or tablespoon of herbs looks like in your palm to conversions to staples to buy before a paddle-trip dopwn a river to simple recipies I like.
NOW, thanks to the above quote, I am making a MER notebook.
This will be filled with my bow-stats, Period references and... vital info like Udwin's formulae for pine glue or how to make oil-cloth to Period foods.
This one will be a home-made booklet or one I find at the renfaire that is small enough for a pouch and looks Period. The one concession will be a pencil or modern pen as dragging out the ink-pot each time i see a great note like this will be a messy pain.