It's the little things, I think- an actor brought me coffee and a bagel at the beginning of our 10/12. Offering to pick up lunch if I can't get out of the theater, etc.
On a superficial level, I love gifts themed to the show- I got a bright (Malvolio) yellow bag with a quote from Twelfth Night on it at the end of that show, a basket of champagne and oranges (referencing the brunch-gone-awry scene) for The Real Thing, and a big box of #2 pencils, erasers, and notebook paper for Children At Play.
Unfortunately, no coins from Rosencrantz+Guildenstern.