A (mundane, real-world) hiker’s reference guide would be very helpful for the travel rules. I don’t know how bad blisters are or how to treat them, but finding info is more useful than making rules about it. References for terrain would also be useful.
Thanks for the thought! I'm currently thinking of having sort of appendices for some of this stuff which, now you have said this, might benefit from also containing a bibliography of relevant useful sources.
I think the terrain things are something I am relatively likely to go into a bit more detail of - perhaps with types of resources/monsters/landscape features etc.