Most of the ingredients I purchased from Target including the candy eyes (Wilton). I bought the black licorice and white air heads at my local Reams grocery store. If you don't want to buy the orange and green frosting, you could always divide the white and use food coloring.
Spider – A great little tip to get easily make black frosting is to add a small amount of black gel food coloring to chocolate frosting. If you start with white frosting you will have to add ALOT of black food coloring. You can either poke the licorice legs into the Rice Krispie or I cut a slit down the side of the Rice Krispie Treat, inserted the legs and then pressed the Rice Krispie back together.
Mummy – I love the way the Mummy turned out. The key is to use white Air Head candy cut into strips. Luckily, my local Reams sells Air Heads individually for .20 each. If you can't find them locally, you can buy white airheads online.
Frankenstein – I used a store bought black frosting to make Frankensteins uneven hair line. You could use frosting to make his mouth and eyebrows but I liked the black licorice best. I used green gummy Life Savers that I cut into small pieces and stuck onto the side of the Rice Krispie Treat. (If the Life Savers don't stick well enough, you can use a toothpick to secure them. Just remember to remove it before eating!)
Pumpkin – I love how orange this Pillsbury Funfetti Orange frosting is. For the jack-o-lantern face I used a sparkly black frosting tube from Target. I like that it shines but any black frosting will do. A pretzel and a piece of a green gummy Life Saver make the stem and leaf. (I only had regular pretzels, a pretzel stick would work best.)