Your signature is required on all your tax returns. As simple as it might seem to just sign it and mail it out, many people forget. Again, it can be a harmless mistake, but it can make someone at the IRS suspect fraud or that you may have forgotten to include other items as well.
Donations can be deducted from your tax returns. Old cars or clothing can be donated, and you can put their value on your forms. However, you need to give a correct amount. You need to be as close as possible to the current market value at the time you donated the item.