It's still probably best to buy your tickets in advanced sadly, especially if you care about where you're sitting. I got out to a game in September and tried to get tickets day of, there was only standing room left. Granted, it was by far the cheapest I've payed for Red Sox tickets in a very long time.
As for bars before the game, most people will tell you the Cask N Flagon. There's a ton of bars on every corner around the park though, so if you're just going for drinks they're pretty much all going to be the same....over priced, and over crowded. I do however really enjoy the Cask N Flagon if I'm having dinner and drinks there. I also enjoy the roof deck at Remy's if it's warm out that day, they got fans blowing mist and stuff.
As for bars not around the park to just go to, it really depends on where you're staying. It's pretty hard to not run into a bar that'll have the game on in this city though.