If a subject catches your attention and you wish to research it using SuperMemo later, simply jot it down on an index card. After you look the subject up and import a few articles into Incremental Reading, you can throw the card away.
If there is foreign language word you want to remember, you can quickly make a paper flashcard and familiarize yourself with the word until you feel comfortable enough to put it into SuperMemo for long-term storage.
They are also useful in giving others your phone number, e-mail, etc. quickly. Today paper is becoming more and more scarce in favor of some sort of electronic device.
I enjoy the act of throwing a "completed card" away, it feels like I am making progress in some intangible way.