Gummy removable glue - attach plastic credit cards to paper
Have you ever seen that special gummy glue, almost, um, boogerlike (for the lack of a better word), that's used to adhere credit cards to paper when banks mail them to you, or to attach products or special cards on the top of magazine covers?
It's not rubber cement, although it is similar. If you use rubber cement in this instance, it will make a far more permanent bond and you will destroy the paper trying to remove it.
This stuff is easy to remove from both plastic and paper, and can be pulled off and wadded up into a little ball (hence my reference to boogers), leaving the paper and plastic intact and clean.
The stuff is called fugitive glue or fugitive adhesive, and a bit less affectionately known in the adhesive trade as booger glue or snot glue.
Since most users of the stuff are printers, publishers, banks and the like, most of what's available out there are large, industrial-size quantities and expensive application equipment.
However, you can buy a more consumer-friendly version called removable glue dots that have about 1/2" circles of fugitive glue on a spool or sheet of wax paper, so they can be easily applied to whatever surface you'd like them on.
Sometimes you can find them at office supply stores, but I've found more exactly what I'm looking for by buying online, via Amazon or one of their associated merchants.
Be sure to buy the clearly-marked removable kind; they also have more permanent versions available that will not pull off paper and plastic easily at all.