Jim brought this up in the Pub, but I thought that since these are for whistle, I’d post them here too.
Here is my list of Whistle Seasonal tunes for this year, with the first few notes.
The First Noel (F#ED EF#GA)
Oh Come, oh come, Emmanuel (EGBBBACBAG)
Hark! The Herald Angels Sing (DGG F#GBAA)
Once in Royal David’s City (DF#G F#GF#GA(B)AG)
Bring a Torch, Jeanette Isabella (dGGF#GABCBA)
God Rest Ye, Merry Gentlemen (EEBBAGF#E DEF#GAB)
The Twelve Days of Christmas (AAAdddCdef#gef#)
Good King Wencheslas (GGGAGGDEF#EF#GG)
Deck the Halls (dCBAGABG)
Have Yourself a Merry Little Christmas (GBdgdCBAGA)
Away in the Manger (aagf#f#eddC#BA)
We Wish You a Merry Christmas (DGGAGF#EE EAABAGF#D)
Joy to the World (gf#edCBAG deef#f#g)
The Holly and the Ivy (DGGGedB GGGGed)
We Three Kings (BAGEF#GF#E)
What Child is This (Greensleeves) (Acdef#edBG ABCAAG#ABGE)
Gloucestershire Wassail (DGAGGABCBABd dCAAACBGBA) or (Adeddef#gf#ef#a)
Sans Day Carol (GBdd dCBG BCAF#G)
Auld Lang Syne (DGF#GB AGA BAGGBde)
Jolly Old St. Nicholas (BBBBAAA GGGGB EEEEDDG AGABA)
Disclaimer: “No warranty, express or implied, that those are right, or that you can find anyone else willing to play them in those keys, but they seem to be working for me. YMMV.” 
