These ideas are from my grandmother's birthday party with the theme of "Over the Rainbow", but if you're using these ideas for St. Patrick's Day, be sure to include the whole "pot of gold" thing, too. :-)
Here's the cake. I made the rainbow with skittles, but in hind sight I think M&M's would have made for brighter colors. The purple skittles were too dark to use, and there wasn't any blue at all.
The cake mix we used was "funfetti", which made it have adorable rainbow spots once we started cutting :-)
Here are our "rainbow snacks"... skittles and rainbow goldfish.
We also had rainbow balloons and streamers! So if you're going shopping today and all the green balloons are gone, now you know what to do ;-)
Happy St. Patrick's Day everyone!