Some of the ones I have run into already with my son and his schoola re check/cheque. airplane/aeroplane, most of the double L words (fulfill vs. fulfil), program/programme, tire/tyre. There are a lot. Pronunciations are even more confusing: A-LUM-I-NUM versus AL-U-MIN-I-UM.
As for religious holidays- I too enjoy learning about the different cultures and things, but let me tell you when your family tree reads like the UN of religions, it's difficult
We have Baptist, Jewish, Catholic, Buddhist, Wiccan, Protestant, and a couple other religions being practiced by members of my family. I usually just end up sending out a rather generic holiday card in December. I have gone to midnight mass (in Latin) with my grandmother at the Catholic church, I have had latkes and ate kosher with my brother, participated in a winter solstice celebration with my aunt, and sang gospel in a Baptist church with my best friend. It's really interesting and eye opening to say the least