Mmm... I'm going to go against the grain here; you just can't carry everything - birds, fungi, plants, insects, trees, knots, trapping, cooking, foraging. On top of that, IMO, the pocket books are rarely good enough to identify some species (especially fungi) with any reasonable degree of certainty. I have difficulty with identification when I have access to my full library in many cases.
Instead, plan your trips to learn about specific things. Take a good book or books with you just on that subject. So in autumn, after a damp spell, go out specifically looking at fungi (ideally with an expert) and a few times of the year (spring, summer, autumn) go out looking at plants etc.
I haven't seen an intro post from you so I don't know how much experience you have, but I think you'll get a lot more out of your trips when they are focussed.
I've just seen Wander's post and I agree - some of those mini books are dreadful; even Food for Free has mistakes.