Dear Godisright,
If you truly feel you need to commemorate this, you can be "safe" with following the Jewish calendar. Pesach (Passover) the Holiday that became the Christian "Last Supper" and the Societies Memorial starts this year on April 12 after sundown. I believe that the Society's memorial is congruous with this as well--many years, it is woefully off and this is always a mystery as they puport to follow so closely the Jewish calendar--one year, they weren't even in Nisan!! LOL!!
Anything with leaven in it (incl) baking soda would be "unkosher" for this event (and Jesus was kosher). Your safest bet is to go to your local grocery store, look in the "Kosher Foods" section and get some Matzoh (these are flat crackers-not too tasty, but not vomitous, either)--make sure it is Kosher for passover--it may say Kashrut for Pesach--that's fine. there won't be any leven.
Wine should be kosher wine (again, there should be a section in a local liquor store with Kosher wines) if you want an authentic what-would-jesus-do experience. It's not too expensive for the "sweeter" versions but you can get some very nice ones from Israel.
Meditate as you recreate, what the "covenant" means to you.
Good luck. And many blessings to you.
~Brigid