Free to a loving home: A box of chemistry and biochemistry flashcards. Some were purchased and some were painstakingly hand-drawn. These took many hours of work and ultimately helped me through to a PhD.
After you're done marking them up and scribbling your own notes on them, pass 'em on to the next poor sucker who signs on for a STEM degree.
Contact by Craigslist email & set up a time to meet at the Black Hawk post office. No weirdness. Just meet during the daytime in a public place with a crap-ton of security cameras. I'll hand you a box of cards & we'll go our separate ways. No strings. No worries. And I absolutely do NOT want to know your phone number.