What everybody else said +

I'm on logbook #6. Not the big Encyclopedia Britannica edition with pages lined with gold but the little Jeppesen deal with the green pages. Fill the one you have then swap. Maybe photograph the last page and keep that photo on a hard drive somewhere. Also, I write "Reward if found" in each one inside the front cover and keep the phone number or address current. If somehow it gets lost or stolen, a crook is likely going to toss it. Whomever finds it may call you. To them it's worth nothing. To you, it's worth everything you've worked so hard for the last few years.