Yes, you can buy bags of fake cobwebs, but save them for inside the house. Their effect will be lost on people driving by and guests arriving at night. Instead make your own giant cobweb and spider or two.
Materials: white rope, stakes, black trash bags, wire hangers, clear tape, stiff white paper
Instructions for Giant Cobweb: Run lengths of white rope diagonally from tree limbs to stakes in the ground. Run lengths of rope diagonally in the opposite direction, creating a woven appearance.
Instructions for Giant Spider: Stuff a large, black trash bag with leaves or crumpled newspaper. Close opening and place it next to the cobweb, shaping it into a spider-body shape. Make a head by filling a bag less full, sealing and positioning it in front of the body. For legs, twist or cut open wire hangers and pull open. Wrap them with black plastic bags and secure with tape. Poke ends into body and secure opposite ends in the ground. Cut circles for eyes and triangles for fangs; secure with tape.
Materials: powdered sugar, chocolate cookies (at least one side all chocolate), black licorice "rope", miniature candies
Instructions: Make edible glue by mixing powdered sugar with a small amount of water. Cut licorice into legs (8 for each cookie). Invert a cookie and spread with glue mixture. Place and arrange legs on glue, then add another cookie, forming a cookie sandwich. Attach mini candies with glue for eyes.
Materials: plastic spiders, ice cube trays (for individual drinks) or muffin tins (for pitcher or punch bowl)
Instructions: Wash spiders. Fill ice cube trays or muffin tins with water. Add spiders and freeze. Serve in cups or add to punch bowl.
Note: Not recommended for small children as the plastic spiders may be considered a choking hazard.