1) lots of drink
2) some pubs do potato cakes and Irish stew (free)
4) if you're a musician and you can play Whisky in the jar, the wild Rover, The galway, Girl, The Soldiers Song, The galway Shawl and The Fields of Athenry on your nose flute and kazoo - you can get a gig. If you can remember how many hogs etc were on The Irish Rover - you can get two gigs.
4) some people wear big hats like a pint of guinness
5)Everybody pretends to be Irish

I think that's everything. Bet they do good potato cakes at The Dorchester.