To help reinforce the spirit of "giving" at a time of year when many kids can't think of anything but "getting," help your kids go through their closets and toy boxes to weed out the surfeit of clothes, books and toys.
Have a gentle talk with your children about the "poor kids," those who don't have as much as you do and need a little help from other kids who have plenty. (You may not, in fact, have plenty, but a) your kids probably don't think so and b) there is always someone worse off than you.) Donate your excess to the Salvation Army, the Goodwill or a PTA clothing closet.
My mom used to tell us that Santa would think he'd already been to our house if he showed up and we had too many toys lying around!