I have a distinct memory from my childhood of my parents arguing in the kitchen after our Passover seder. They realized after clearing the table that my family members had drank the last of our wine and we had nothing to leave out for Elijah. My dad suggested we could leave a can of Coke, and my mom shrieked, “You can’t leave COKE for ELIJAH!”
now you can 😛
There is a halachic classification of beverages called chamar medina (literally, “the national beverage”) which refers to non-wine beverages that are nevertheless considered “respectable” enough to be the bedi’eved (not ideal, but still halachically permitted) liquid used for kiddush, havdala and other ritual uses.
Classic examples of chamar medina are beer, coffee and tea. While some authorities¹ don’t consider soft drinks to be “respectable” enough, others² do.
The Four Cups themselves are actually obligatory; Elijah’s Cup is merely traditional. So while I would suggest using Kosher-for-Pesach Coke (made with cane sugar, not corn syrup) for the Four Cups only as a last resort, I imagine one could rely on chamar medina to Share an Ice Cold Coke with Eliyah.
¹ Iggros Moshe (R’ Moshe Feinstein)
² Shearim Metzuyanim Behalacha 5:page 74; Rivevos Ephraim 3:290, and p. 358, citing from a number of authorities
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