A good pair of scissors is imperative. Don’t use them for anything else but cutting cloth. Joanne’s has a scissor sharpening service and it’s really worth it when your scissors begin to dull. A tip on cutting a straight line is to snip a section where you want to start the line, and pull out a string or two as if you were gathering the fabric, this will give you a perfectly straight line in which to cut. I also keep a pair of smaller scissors next to the machine to clip threads. I always thought a rotary cutter was more for those who do quilts, but I don’t know.
Besides my scissors, my most useful tool is my seam ripper! Have lots of bobbins so you don’t have to take the thread off a bobbin to use a new color. I like straight pins with a bulb on the end, there are easier to use and if they fall on the floor they are easier to see. If the room you are sewing in has carpet, you might want to get one of those Mr. Sticky rollers. It picks up loose thread which can be a bear to get off the roller bar of your vacuum. Measuring tape and a small sewing gauge are useful. Velcro in all sizes, but I only buy black and white.
I usually buy thread with my fabric at Joanne’s, but Walmart has better deals on thread than Joanne’s. Note how many yards the thread has, I usually buy all purpose thread and tend to use black and white the most. I buy my d-rings online, they are smaller than the ones I can get locally.
D Rings, nickle plate, 8 sizes, 2 styles, Welded or Cast
I agree that an iron is important; I iron folded seams before sewing. If you are buying an iron, don’t get one that shuts off every 5 minutes, you spend all your time waiting for the iron to heat.