This is my season! I know I'm not alone because readers of my Halloween book "Adult Halloween: Taking Back the Season!" tell me that they get more excited about Halloween than Christmas!
Most of these things you probably have around the house and from Halloweens past. Other items are cheap or free to obtain. Take advantage of the dollar store and thrift stores - no need to get fancy.
Stock up on items that can be used every year -
cover furnishings, make tattered curtains, create costumes, make a blanket fort for scary movie watching, create tablecloth with creepy magic marker drawings on it
tape to a wall and use chalk and a shoebox (as a template) to trace castle wall bricks, create a backdrop for selfies, use fluorescent paints and a black light to make a crazy wall)
making ghosts, draping a mask or mannequin, casting a colored light through it, covering a styrofoam head, costuming
decoupaging, fabric stiffener, making slime