DO NOT travel with your Social Security card or use it for identification: your Social Security number is a fast lane for identity thieves.

As it has no picture, expiration date etc. it doesn't fulfill TSA's criteria anyway.

By law you are not required to disclose this number to any entity but the IRS and employers, etc. who disburse funds to IRS on your behalf (i.e. taxes withheld from your paycheck). Keep your card in a safe place; they are a real pain to replace these days. Replacement SS#s are rarely given even when ID theft is proven.