If Christmas is your holiday then it's totally understandable that you would choose to buy CHRISTMAS cards and merchandise. I wouldn't expect anything else and I have no interest in trying to convince you to choose "Happy Holiday" stuff.
I understand your preference for "Merry Christmas". I just don't get the hostility towards "Happy Holidays". When you use "Merry Christmas" you aren't trying to knock Hanukkah or force the other person to accept Christ, right? You're just expressing kindness and good cheer to the other person. So why do you assume that someone using "Happy Holidays" is trying to knock YOUR holiday or trying to change YOUR beliefs?