On the basis of what I miss most if I don't take it (them)...
My Binoculars.. it doesn't matter whether I'm hillwalking, bushcrafting, walking the dog , whatever... and not just for watching birds, butterflies or other beasties although I do a lot of that... They save my legs by helping pick the right route, or help me check out plants, or ID trees in winter by looking at the buds.. and the ripeness of fruit.. or those tracks in the mud across the river.. and of course they give me an extra half an hour of daylight if I'm out at dusk.... and of course you can see a lot more stars with them.. and then... well you get the picture!