For those of us with (some) Irish heritage, sometimes the day is a day to make traditional foods - soda bread, and potato dishes, and corned beef (which is actually more Irish-American, and isn't something I care for anyway, even if it weren't too high in sodium - lamb or mutton is actually more "traditionally" Irish).
In recent, recent years, among Pony fans, Lyra has kind of become the unofficial St. Paddy's Pony. Partly for her color scheme, partly (perhaps) for her lyre (Irish harp? not quite the same shape) cutie mark.
Here's a cute example, from Contreras19 (who has specified sharing is okay with credit):