I kept all my prompt books from college as it was a momento and i figured somoene might ask to see a sample of my work. But as somoene mentioned in another thread how often are you really asked to show a prompt book in an interview, your prompt book can show a little about your organizational skills but ultimately somoene can have a greatly organized binder but suck as a stage manager, you really just have to talk to somoene enough to see if they would be good.
But anyway I keep mine from college and its fun flipping back to some and seeing how poorly I did with them and then look at my current one and be like "what the hell was I thinking then" and it seems with each show the binder improves a little more. So as I start my journey into the real world I am actually working on my first show where they say in the contract I have to turn the script into them. So what I have is my own binder with tabs laid out that I'll use for everyshow I do (its a spiffy binder that has some extra pockets, a four tab file folder thing on the front cover, pen/pencil holder, zippers up, and has a flap on the front that holds a small notepad on the front which is very useful to jot down a quick note when you pass someone in the hallway or something.) So I have all my tabs laid out and when the show closes i can take out all the info keeping my tabs and hand it into the theatre (i figure they can supply their own binder or an envelope to keep it all in, but given somones suggestion here I will probably add in post it tabs to break down the sections). Then when my next show starts I can just begin filling in my tab sections with new paper work. I don't know if I'm gonna try to keep copies of all my prompt books cause when I look around at the box of ones I have from college I think all they do is sit in a box taking up space do I really need them. I know there are some shows I will keep though.