Well, if you're flying hand-luggage only you can't bring anything back with you.
If you're bringing checked-in bags and are staying longer, you might be able to make the journey to Utobeer in Borough Market. Nearer the V&A there's House of Fraser (FKA Army & Navy) at 101 Victoria Street, though it's still a bit of a walk.
And of course any damn Tesco or Oddbins in the UK will have a better selection than even the most specialised beer off licences in Ireland.