The minimum it takes to sew is a needle and thread. However, some additional sewing supplies won't hurt your creative efforts.
To start, and to sew by hand, you need a kit that contains, at bare minimum:
Scissors of different sizes, pins, needles, thimble, tape measure, spools of thread, chalk
As you move on to more ambitious projects, you'll find that you need to add some more specific equipment to your sewing box.
Open sewing basket, with basic supplies
Watch this demonstration to learn the basics of using a sewing machine.
Remember that these supplies, sometimes expensive at purchase, can last for a long time if you use them well.
Thread nipper
Needles and pins also need some attention.
Tracing wheel
Always use a clothes iron for your work: it's an indispensable ally for successful sewing.
For ambitious seamstresses (and seamsters), here's the list of supplies necessary for the different stages of creating clothing items.
Scissors of different sizes, thread nipper, pins, magnet, needles, iron, thimble, tape measure, spools of thread, chalk, tracing wheel, French curve