Despite my epic struggle with Joyce's Ulysses (posted here and here, if you care), I'm happy to celebrate the day on which the book's events take place.
What's especially nice about Bloomsday is that there are so many possible ways to celebrate in the traditional manner: by emulating Bloom's conduct. This is a book that (rather famously) has everything. Hence the obscenity charges.
Very plausible ways to celebrate include eating a breakfast of panfried kidneys, rashers, sausages, bean, black & white puddings, and toast, or a lunch of gorgonzola sandwiches accompanied by a glass of red wine. One could stop in at a newspaper office, use an outhouse, attend a funeral, walk on the beach and ogle the girls, buy some soap at a drugstore, visit a brothel, participate in a discussion about Shakespeare, hang out in a pub, or bring home a drunk friend to keep him out of trouble. Or (although technically this is Mrs. Bloom's pasttime) one could loll around in bed and think about sex.
Like I said, it's pretty much all in here. So many ways to celebrate.