Paperback books - 50 cents, less if no one is buying any. If they're really beat up, charge 25¢, books aren't usualy great sellers. Everything else depends on what kinda shape it's in, and what prices are normal in your area. Separate the "real" from the "costume" jewelry, put all the jewelry in one area so it doesn't get "lost" amidst the rest of the larger items.

Put up a sign that all proceeds go to charity, and tell people they can pay as much OVER the marked price as they want. Smile as you say it! Have hot or cold (depending on the weather) drinks available for sale cheaply, people will linger longer while they sip.