It is always a good idea to ask your hosts what you can bring for the seder, or the dinner. Your host might ask you to bring the hard boiled eggs, the kosher horseradish, a vegetable dish, grape juice or kosher-for-Passover wine. If they don't specify what to bring, it is still nice to bring kosher-for-Passover candy or chocolates (found in many grocery stores at this time of year), flowers, or wine (the bottle must say it is kosher for Passover). Remember, if you are preparing a dish, it cannot contain any flour or grain (wheat, barley, rye, spelt or oats) or it must say that it is kosher for Passover on the box, and, probably best to check with your host about their level of observance.
See also: What to Expect at a Passover Seder