It depends I guess on what kind of hair bows you will be making. For any bow maker a great pair of scissors is a great start. I know it is overwhelming at first with what to buy first and what you will need first, etc. Decide on which style you are wanting to work with first, what size, etc. and go from there.
Items I cant do without for my flower making and stacked hair bows are...glue gun, upholstery thread to sew my flowers and bows together with, 1.5 inch ribbon, 7/8 inch ribbon and 3/8 inch ribbon, hair clips, and Sally's salon clip.