There definitely are two types of potlucks: "go all out" and "anything will do." Fortunately, I don't go to too many of the latter, but in those cases, frozen dim sum nuked in the microwave sometimes seems sufficient. I'm totally against the "sneaking in a bucket of chicken" trick.
In the first category, I once met a friend and went shopping for a few hours in the morning, had lunch, had drinks, made two somewhat complicated dishes, and arrived two hours late to the party. Fun day all around, and actually lots of good leftovers.
Back to reality: a dish that is extremely attractive and not terribly difficult to make, but somewhat time-consuming, is the "quick gravlax" in the cookbook by Julia Child and Jacques Pepin. Traditional gravlax is made with a thick piece of salmon immersed in a salt-and-sugar mixture and needs to cure for several days. In the quick method "adapted for potluck" you do the following the night before:
(1) chunk of salmon (half pound will do);
(2) transparent plastic plates;
(3) topping ingredients you don't already have.
(1) Thinly slice the salmon on an angle to make pieces about 2"x4";
(2) Sprinkle lightly on both sides with kosher salt and white sugar (I forget the exact quantities);
(3) Arrange on plates for service (e.g., overlapping slightly) and press plastic wrap over to exclude as much air as possible; refrigerate until ready to serve;
(4) Prepare toppings to be added at the last moment.
For toppings I have used:
(A) Light drizzling of dark Japanese sesame oil, which makes the salmon decadently rich, but could be too rich for some people;
(B) Chopped fresh dill or other complementary herb;
(C) Light drizzling of honey mustard thinned with rice vinegar.
If you think about the versatility of salmon, the possibilities really are endless.
I think the difficult question with this dish, after getting the smell off your hands (try a lemon wedge), is what "quality" of samon you should use. Is it really okay to use the inexpensive jumbo slabs of Chilean farmed Atlantic Salmon from Costco, or do you need to select the expensive sashimi-grade salmon at your local Nijiya market? To my knowledge, this dish was developed to be made with ordinary cuts of fish, so I use farmed salmon without guilt. Of course, as with any raw fish, it needs to be fresh and if you see anything suspicious while slicing, don't serve it.