As it happens, I did forget today's holiday until now, but luckily ate cereal anyway.
The festival of "Cerialia" ("Cerealia"? The spelling seems several.) is a particularly entertaining one, what with the exchange of hospitality among the common people and the letting loose of foxes with burning torches tied to their tails[1]. What a sight! We'll have to see if we can hunt down a fox today that we might try it!
Today is also St. Alphege's day. He seems to be the chap who persuaded Svend Tyggeskaeg (aka "Forkbeard" - geez those Vikings knew how to slap a nickname on their marauders) to stop raiding England. So today we eat cereal and celebrate St. Alphege's stand for peace and, if we can find a fox, we'll tie a torch to her tail this evening. (Hmm, wonder if Sadie would go for it.)
[1] Blackburn et. al., Oxford Book of Days, p. 160