Trademark Statement of Use

As the others have stated, the general rule is one specimen per class. But beware that if the classes describe a long list of goods/services, or describe "a whole line of _________" goods, the USPTO could require additional specimens for additional goods. Also, remember that when you sign the Statement of Use declaration, you will be swearing under oath that the mark is being used on all of the listed goods/services, not just one per class. While the USPTO may not check that, if you in fact are not using the mark on all of the listed goods/services a third party could attempt to cancel your resulting registration based upon that alleged inaccuracy or untruth before the USPTO.