Not necessarily bushcraft but IMO deserves a mention;
The humble fountain pen. Chose this one, the Esterbrook J, in particular as it is a simple, sturdy and flexible design from the 50s.
Funny you should say that, I have recently started using a couple of chinese knock-offs of the venerable parker 51. Coupled with waterproof ink (noodlers bulletproof variety), they serve me very well in taking notes when out and about.