A free gift is one for which the giver is not trying to get something in return, or one which does not cost the giver, such as when it is discount on resulting sales.

In 19th Century Saloons

The phrase free lunch, in U. S. literature from about 1870 to 1920, refers to a tradition once common in saloons in many places in the United States. These establishments included a "free" lunch, varying from rudimentary to quite elaborate, with the purchase of at least one drink. These free lunches were typically worth far more than the price of a single drink. The saloon-keeper relied on the expectation that most customers would buy more than one drink, and that the practice would build patronage for other times of day.

Grammatical Error

The word "gift" is already suggesting that it is given to the receiver for free. Adding "free" before the word "gift" does not make any sense. You would not see the word "free free item".

See also

• Free lunch
  Free lunch
  The phrase free lunch, in U.S. literature from about 1870 to 1920, refers to a tradition once common in saloons in many places in the United States. These establishments included a "free" lunch, varying from rudimentary to quite elaborate, with the purchase of at least one drink. These free lunches...
  
  
• There ain't no such thing as a free lunch (TANSTAAFL)
• Opportunity cost
  Opportunity cost
  Opportunity cost is the cost of any activity measured in terms of the value of the best alternative that is not chosen . It is the sacrifice related to the second best choice available to someone, or group, who has picked among several mutually exclusive choices. The opportunity cost is also the...
  
  
• Externality
  Externality
  In economics, an externality is a cost or benefit, not transmitted through prices, incurred by a party who did not agree to the action causing the cost or benefit...