"Christmas Gift!" is a GREETING traced back to the early 1800s in the southern United States. It is derived from tradition of waking on Christmas morning and rushing to say "Christmas gift" before anyone else. The person being told "Christmas gift!" is expected to present the person saying it to them with a present.
While "Merry Christmas" is the common and current seasonal salutation, "Christmas gift" was an equivalent expression used in the rural south and also in southern Pennsylvania, Ohio Valley, West Virginia, and later in northeastern Texas as a simple greeting and recognizing the birth of Christ as a gift.
The greeting is first attested in 1809.
"Christmas EVE Gift" is similar, but on Christmas Eve, one being told "Christmas Eve Gift!" is expected to give a small present, traditionally candy or nuts.
In Slavic mythology, Perun (Cyrillic: Перýн) is the highest god of the pantheon and the god of sky, thunder, lightning, storms, rain, law, war, fertility and oak trees. His other attributes were fire, mountains, wind, iris, eagle, firmament (in Indo-European languages, this was joined with the notion of the sky of stone), horses and carts, weapons (hammer, axe (Axe of Perun), and arrow), and war. He was first associated with weapons made of stone and later with those of metal.