Because this is college, right? When it comes down to the bottom line the best alcohol to bring to a college party is cheap beer. I am not talking $20 30's like Coors Light, I'm talking in the $14-$18 range like Natty Light or Keystone. Why, cheap you ask? Because on the whole we are all pretty much poor. Plus, if someone snags your bag full of beer its much better to have it be full of Keystone Light and not some Sam Adams or something nicer. One knock about beer is that it tends to go fast. Between two roommates a 30 probably won't last a full weekend (especially if you're including Thursday nights). A big handle on the other hand is much more likely to last longer. Also with beer, it is much more tempting to have a couple during the week and with cheap beer that can be a waste if you're not getting wasted.
On the other hand beer is much better to bring to a party since you can drink more of it. Brining a water bottle with cranberry vodka is not going to last long at a party, especially there are a lot of drinking games going on. That brings up my next point about cheap beer, it is the best alcohol for drinking games. Whether it is beirut, kings, asshole, fuck the dealer or any other game, beer is the way to go. If you're playing a drinking game with rum or vodka or any type of hard alcohol you'll be lucky to last a game or two. While Natty Light and Keystone Light seem to be the campus favorite cheep beers I actually prefer PBR.
Personally, I think PBR has a better taste than most cheap beers, despite it's high carbonation. Most cheap beers taste very watery, while PBR does have a little better flavor. It also has a slightly higher alcohol content (5.7%) compared to most beers in it's price range and quality. Keystone Light is only 4.2%. But at the same time PBR isn't a light beer so that would make sense. Most light beers are in the low to mid 4% alcohol range, but heavier beers are usually around 5% (but range up to 10% or higher).
Since PBR isn't a light beer it has 50 more calories than Keystone Light. Drinking a lot of cheap beers will result in mass drunkenness and probably a decent hangover, but what do you expect? You get what you pay for. Most cheap beers are pretty similar, I just like the slightly higher content that PBR has to offer. When it comes to light beers, I would put Keystone just ahead of Natty. I know that everyone has their preferences, but let's face it cheap beer is cheap beer.
Stay classy, not UMassy.