I'm probably not going to be much help, because I'd just show up with a case of Bud Light . It's low hanging fruit, but there's a reason you can always get a Bud Light in most bars - it's popular. I'm certain beer aficionado's will disagree, but I'm used to that! Of course, there are the other "go to" beers, such as Corona (with a lime), and I always keep Red Stripe (Jamaican), Miller Lite, and Narragansett (Boston) in the garage fridge for a change or friends. On occasion I keep Devil's Backbone Vienna Lager or Sam Adams on hand, both good drops. I'm certain others will chime in with IPA recommendations, but since I'm more of a pilsner / lager fan I don't really like the heavy hops in IPA's. IPA drinkers are always glad to tell you about the seemingly endless varieties and how they are far superior to commercial beers.
But to your 4 specific questions:
1. Holiday cocktail - Sam Adams has seasonal small batch brews, like a winter or Oktoberfest. Those seem popular. There are also some decent ciders such as Bold Rock (not widely available, from a brewery outside of Charlottesville VA or more widely available Angry Orchard. These hard apple ciders are technically a beer and popular with people who don't really like the taste of beer.
2. Summer party - this is where I would show up with the more common Bud Light, Miller Lite, or Corona's. If it's a graduation with college aged kids Pabst Blue Ribbon is surprisingly popular (low cost, making a comeback).
3. Family crowd - bourbon. You haven't met my family.
4. Beer fan - here is where I'd risk bringing IPA's. You can usually get mix and max packs at most grocery stores these days, and places like Total Wine have more varieties than you can imagine. The staff at the stores like this can probably make recommendations.