I definitely agree with Andy’s post above of the 50 Christmas Carols arr by Sylvia Woods! That is a great Christmas book to have is full of lovely easy to play arrangements!
In addition, on of my favorites is from another collection of hers – I love the Silver Bells arrangement from her ‘Four Holiday Favorites’. It has Silver Bells ( so pretty), Frosty the Snowman, Let it Snow and Rudolph the Red Nosed Reindeer (another of my favorites to play!).
All good suggestions, here’s another: Cynthia Shelhart’s “Tunes to Go – 400 Tunes in Lead Sheet Format”. I’ve not counted the number of Christmas tunes but there must be well over a dozen out of the 400 popular tunes.
Lead sheet format is nice – depending on your ability and venue you can arrange to suit and this also makes it easy to change the key if you don’t want to use what Cynthia indicates.
There are some lovely Christmas arrangements at music discoveries by Anne Crosby Gaudet. They are all viewable as a pdf preview and have videos so you can hear the whole thing before buying. Christmas Music
For real beginners my students enjoy this book a lot.