While you can write off donations on your taxes, there's still a limit to how much you should give away. Only you know your financial situation. Depending on the organization and how they're promoting it (I'm assuming it would be a raffle or action), it could be good publicity. However, while donating a pair of my guitar pick earrings would be no big deal for me, your jewelry is rather more expensive than that. If you don't feel like you can afford to donate something, just politely but firmly tell whoever is approaching you that although you support their cause, you've donated all you can this year.
Also, are these people approaching you in person or via Etsy? I believe it's actually against Etsy's TOU to solicit donations. I'm also wary of anyone asking for free stuff online, whether they're bloggers or supposedly working on behalf of a charity. Then again, maybe I'm too jaded.