Hey-
As a native Bostonian, the South Boston Parade is THE event of the year! Great choice! Take the T (our subway system) the Red Line to the Broadway stop to get up onto the parade route. Don't even THINK about driving or taking a taxi. They shut down all the roads in and out of South Boston. Trust me. Take the subway. It's perfectly safe and totally worth it. Be warned - it stops running altogether at 1AM. A couple of other things to do while you're here:
1.) Trolly Tour (for one price you can get on & off the trolly all day)
2.) Observation deck at The Prudential Center (awesome views)
3.) Fanueil Hall (tons of bars, resturants & shopping)
4.) Tour of Fenway Park
5.) Legal Seafoods at Copely Place (NOT PRUDENTIAL) at sunset
6.) Pizzeria Regina in the North End b4 the game
7.) Mike's Pastries in the North End after the game
8.) Umbria, News, Whiskey Park (Ultra-Lounges)
9.) Union Oyster House
10.) Walk the Freedom Trail
Good luck & have fun!