With the advent of fertility drugs and sooo many multiple births these days, sorry to say, but true "freebies" for twins are few and far between. Look in the paper for a local moms of multiples club. These groups often have huge rummage sales which are a bonanza of all things for twins and more. Her hospital and/or medical center may be able to refer her to support groups and places for help.
Ask around to see which catalog companies or baby websites have multiple discounts. I know that One Step Ahead / Leaps and Bounds has one. When you mention you have twins (or type TWIN in the discount code area), you get an automatic 10% off your order. It's not much, but with some of the clearance prices on their website, you can get some good deals.
One Step Ahead
The local fire department and police department will often run programs for free or low cost car seats and restraints.