One of my favorites to bring when I have the room is a nature handbook that has illustrations and and region maps of all North American animals and plants located in the area. It's more of a tradition to bring it with me- not exactly something I start reading while walking around in the wilderness. Still, it's a great reference, especially because I'm not always familiar with the plants in the area and want to know what they are.
How about you all?
How about you all?