Did someone say “Free books?”
One of the recently completed PhD students here in physics just sent an email around advertising free books - as soon as I got it (Gmail notifier checks every 2 minutes!) I headed down there (”Aha! It’s only at the end of the hall!”) - and there was already a crowd of physicists hunting through the pile! Pretty good turn out, really 
I picked up an ancient edition of Volume 2 of the Feynman Lectures - a fantastic series of lecture notes that work as both a great teaching course and a reference text. I’ve already got a full set, but they’re so good that I might give it to someone (a physics someone!) as a gift. It’s not pretty, though - it has a very “typewriter” look to it, but never mind!
My favourite line, heard from a hovering postdoc: “Any free food, or just books?” How very appropriate. Although I thought my seagull impersonation as we all descended on the books was rather amusing too