Beside my machine the most used are the cutting mat, rotary cutter, 12 x6 and 6 x 24 rulers. But I have many items that I use and love.
Bent pins with covers for basting. A 16 in square ruler for squaring up quilts.
Wooden skewers for holding pieces when sewing. Small scissors for cutting threads.
A sewing cabinet where my machine sits even with the top, makes quilting so much easier.
Travel iron for piecing and big iron for large fabrics. Eleanor Burns flying geese rulers and many of her books.
ect. ect. ect.