Vegan holiday baking
First of all, that's very sweet and considerate of you.
I usually use non-vegan recipes and substitute as needed. If your co-workers are strict vegans, you should also avoid refined sugar, as some of it is processed with bone char. The cane sugar granules that are the size / shape of sugar work well as a substitute (I don't avoid refined sugar, and still prefer that stuff).
Even though it's like $5-6 for a box (which will last for a *long* time - it'll probably go bad before you run out), I'd suggest getting Ener-G egg replacer (available at most health food places). It's a powder made of potato starch, tapioca flour, and some other random stuff. In many cases, you can just mix it in with the dry ingredients; otherwise, you mix it with water (1.5 tsp egg replacer / 2 Tbsp water). One little trick - it will work better if you add a tiny bit of extra baking powder if the recipe calls for it. Like 1/8 tsp or less extra.
The main other egg substitute I've seen people use is flax seed.
For dairy, replace w/ almond milk or soy milk, and for small amounts of butter, you can use non-hydrogenated margarine sticks (like Earth Balance), or else oil.
Not super holiday-themed, but I made some really good chocolate cupcakes with hazelnuts, with chocolate frosting and raspberries on top. I kinda threw the recipe together from a few different recipes online; they came out great.
My family has this cookie making party every year that we've been having since I was 1; my mom makes these sugar cookies (these days she just makes all the dough without milk or eggs, even though the original recipe calls for butter), and they taste great - no one ever complains. I can try to get the recipe if you want, but they're pretty standard sugar cookies (the recipe is probably from James Beard, Fannie Farmer, or some other old cookbook).
I used to do a fair amount of baking for vegan friends- here's a recipe for sugar cookies that is easy and tasty.
1 1/2 c. sugar
1 c. vegan margarine (such as earth balance)
3/4 c. soy or rice milk with 1-t. vinegar added to make sour milk)
4 to 5 c. flour
1 t. baking powder
1-t. baking soda
Mix dry ingredients together. Cream margarine (or replacer) and sugar. Add soured milk alternately with dry ingredients. Chill dough for 1 hour. Cut dough into quarters and roll, one quarter at a time. Do not roll too thin! Cut into desired shapes. Sprinkle tops with sugar. Bake at 350 degrees for 8-10 minutes. DO NOT BROWN
I veganized the Chocolate Spice cookies from "Perfect Light Desserts ..." by Nick Malgieri and David Joachim. The recipe is available on Kim O'Donnel's blog here:
I used olive oil instead of butter. Earth Balance is a better substitute but I ran out. The cookies still turned out great; nice spice and chocolate flavours.