I personally find it much easier to transport food if you are leaning more toward keeping is cold...also I try not to bring anything that has to be heated, as the hostess might not have room to heat another dish... I have taken BBQ Pork, Reg. Chili and White bean chicken chili, and potato soup in my own crock pot and traveled but under the 1 hour mark.
I make a tray, using several kinds of Olives, a few types of Pickles, Giardiniera, now you can find pickled okra, green beans, Asparagus, and those baby corns.
Homemade dips of some kind... everything from basic ranch, clam dip, salmon spread, spinach dip, veggie cream cheese spread... Then hit up somewhere that has fancy crackers..
I think some already said the pretzel rods, dipped in chocolate, and sprinkles...
I did Oreo's one year and really any sandwich style cookie will work, melt reg. or white chocolate, sprinkles, chocolate chips. This works great for a big crowd... Aldi or Wal-Mart for cookies and a double boiler for the chocolate, get the kids to help with the sprinkles your good to go...
Any kind of pound cake... during the holiday's I will make lemon pound cake.... no frosting if I am taking macerated berries, or make a glaze... sometimes for me with all the heavy dessert during this time of year .... having something a little lighter is nice. I sliced the cakes putting them on those throw away silver trays, put the berries in a plastic bowl in a small cooler with ice packs, and a take a nice bowl to put them in next to the cakes, Once there I pour the berries into the bowl, put the plastic bowl back in the cooler, throw everything back in the car and enjoy the party.
Another trick I use is I normally pick up some odd and ends bowls, plates, platters... at Marshalls, Ross, Home Goods, TJ Max , Tuesday morning or wherever knowing that I am leaving it for the hostess, so when I get ready to go I can just go and not worry about my dishes.. Check the clearance areas... I scored a couple of nice etched glass bowls for under 5 bucks each and a couple of Christmas plates for like 2.99 each... and a nice platter for 12.00 dollars normally I don't spend that much, but it was for a friend that had recently got divorced and was starting over.