Jake, I love these ideas!
The better word you are looking for is "tzedakah", which means what you mean to say by "charity" but instead of being related, etymologically, to a subjective and interior feeling of caritas, translates literally and simply as "justice".
Better than worms, our kitchen scraps go into the municipal industrial compost which captures the methane and generates electricity from it.
I am interested in hearing more about your suggestions for development-oriented tzedakah; that is definitely a crucial element, and you probably have a much better idea than I do what's effective.
To clarify a little where offsets fit in: we have a "tzedakah" budget, which is simply a set amount per month, and which has to address all the things we'd like to fix about the world, from disaster relief to long-term development to less economic forms of social justice and political action (like, say, Americans for Peace Now).
On top of that, some of the money we can't afford to give away but don't need immediately, we park in Kiva as a form of zero-interest savings. As with offsets, Kiva's model of microcredit has some risks, gaps in transparency, and possible perverse incentives, but I think on balance it is a reasonable way to have that money produce some marginal improvement in economic justice, as lack of access to credit is one thing that keeps our Haitian woodburner from upgrading.
This offset idea is, from a "family accounting" perspective, a third thing. Rather than being linked to income or cash flow, it's connected to, for instance, travel expenses. So when sitting down to think out "how many trips will we take this year and how much will they cost?" the idea is to factor into the financial equation some of the externalities.