My favorite is a wooden awl that my husband made by mistake while doing some woodworking. He was showing me some pieces he had made and I knew I need one and just what I needed it for. It comes in handy when I am pressing small pieces.
I must admitt my most used notion is the seamripper.
My granddaughter rook sewing in school this year. One day I asked her how she like seewing. Her answer--Gramma I am becoming best friends with the seam ripper.