St. Patrick's Day Party
Make shamrocks from construction paper of all shapes and sizes and tape/hang them around the room.
Use a witches black cauldron and fill with rocks painted gold. Then using different color streamers create a rainbow starting at one end of the room and tape it up in the center of the room creating the arch... you might have to tape it in a few places to get the round shape of a rainbow... then have it end at the pot of gold.
A St. Patrick's Day party wouldn't be complete without the traditional GREEN food. You can use green food coloring to tint your food.
Party favors could be anything symbolizing LUCK like... shamrocks, kiss me I'm Irish buttons, rabbit feet or everyone can paint their own blarney stone and take it home as a favor.