Pick a charity and have you and your group/convention do events to support it.
This is probably the simplest thing you can do, but it’s also effective. Almost any major geeky con has an associated charity or two, raising money for them with sales, donations, auctions, and so forth. It’s almost an afterthought.
Of course it shouldn’t be an afterthought – clubs and cons and the like can do a lot of good. It doesn’t even have to be raising money – maybe you rally your group to work phones, or gather books or school supplies, or whatever you want to do or try. Find the right cause and get imaginative.
You could even get creative with all sorts of theming and synergies:
- Do a blood drive at your vampire event.
- If you’re a fanfic group, donate time to maintaining the website for a good cause.
- Your literature-oriented convention could promote literacy (and maybe give people a chance to join a literacy organization)
There’s too many suggestions to even try at this point – but remember it can’t hurt to pick something relevant and give it a try. Your only risk is doing less good than you intended . . . but always do more than doing nothing.
Oh and if you don’t have a group or organization that’s charity inclined? Do it yourself. Better a $10-a-month donation off your credit card than nothing. Besides that monthly deduction can keep reminding you there’s always more to do . . .