Pubs, bars, clubs, musical instruments shops...
In the meantime, let me find a link to a thread from recently where a number of us had a massive masturbation over the awesomeness of the Weeg.
Nice n Sleazy (pub)
Mono (pub)/Monorail Music (record shop)
I think there's an aftershow for the Sad gig at The Flying Duck.
Biggest one left in Glasgow is actually pretty good, it's called Guitar Guitar and is on the Trongate which is actually on the way to the Barrowlands. Fair enough, it's mostly guitars, not sure what instrument you play...
Drinking wise, Sleazy's and Mono that capt_oats suggested are good shouts. I'd also recommend republic bier halle which just off Buchanan St across from TGI fridays, they do hundreds of different beers and 2 for 1 pizza's that are incredible!
Who have PINS playing on the 15th too, but it's a late starter. Variety Bar is also a good shout.
Best not to drink in the bars around the Barrowlands as they're all old firm football pubs and a few of them can be a bit rough. Get drinking in town then you can either walk down to the venue or get a taxi.