Congratulations on wanting to help such a great organization! They provide so much comfort for folks!
One thing I've knit a lot of are various patterns for fingerless gloves. They're simple to knit if you get an easy pattern and everyone I've given them to loves them. You don't have to be a teenager to appreciate having fingers free but hands warm for cell phoning, driving, texting, making change at the supermarket, etc. etc. etc. I'm sure there are tons of patterns available that would be fast and easy to make. You can also make them out of worsted weight for great winter warmth.
The other thing I did with mine was I had learned to knit two socks at the same time on one long cable needle and that's how I did the gloves. When they were done, they were both done and they seemed to go very quickly. Melissa Morgan-Oakes has a book with the technique for 2 at a time on one needle socks but you can use that method for anything you need two of, even sleeves for sweaters.
Good luck with your endeavor and let us know how it goes!