I ended up getting a bad cold and feeling horrible, so we ended up just getting chips and dip from a Mexican restaurant, some stuff from the grocery store that just needed to be heated up, and then did a salad and fresh berries.
I ordered little sombreros and maracas from Amazon.com, as well as some cute candles to put on the cake (sombrero, cactus, maracas, etc).
He had a blast and everyone thought it was really cute.