My newest obsession is Hidden Note Inserts. There are lots of videos and instructions out there. I used this video.
I made these for the recent Junk Journal Add-In swap.
I used some patterned scrapbook paper and then collaged on the fronts. the backs (but not the top section of the back) is meant to be glued down in a journal. and then you have a cute little note you can write on and then stick back in.
I used old library cards for the note paper but you could use anything.
And a bonus decorated paper clip