This is a hoax. As usual these hoaxes are targeted at those that are not yet cynical enough ;-) There is no such promotion it's just a hoax.
Subject: FW: Cracker Barrel Gift Certificate
My name is Junior Johnson, founder of Cracker Barrel.
In an attempt to get our name out to more people in
the rural communities where we are not currently
located, we are offering a $50 gift certificate to
anyone who forwards this email to 9 of their
friends. Just send this email to them and you will
receive an email back with a confirmation number to
claim your gift certificate.
Founder of Cracker Barrel
Hey guys, DONT DELETE THIS EMAIL It really works,
I tried it and got my Gift certificate and
confirmation number in 3 minutes.
Please ignore any messages regarding this hoax and do not pass on any messages regarding it. Passing on messages about this hoax serves only to further propagate it.