Date the notebook itself (on the inside cover, when you started it and when you finished it) and date the entries. You can use one date for each day's thoughts, poetry, etc. Yes, just skip a line or two. Use office supplies to denote random thoughts or poetry or whatever you write. That's what I do.

I got the idea of dating the journals themselves from work, where we had to fill out log books. It makes them easier to organize if you generate a lot of material as we did.

I currently have five journals organized by the dates I opened them. They're also numbered one to five in the order I've generated them. It's redundant, I know, but that's for quick reference.

It's so much easier to have one place for everything.