Embroidery floss. We can use classical cotton threads, or embroidery floss that is stronger. You can also use threads with different thicknesses to make the bracelets different. I personally use cross stitch embroidery floss and highly recommend it, on the other side, I certainly don't recommend using wool. Bracelets from wool aren't nice, I don't like them at all.
What is also very important is that the strings need to have the same thickness. Never tie a bracelet from three classical cotton threads and three cross stitch embroidery threads because the bracelet wouldn't look any good.
Safety pin, with the help of safety pin, we fasten the bracelet to some kind of mat - knee, pillow or something else.
Scissors, to cut the strings with.
You don't have to limit yourself to bracelets with string only. You can do all sorts of stuff, from adding beads to making key-rings and badges. In the photo above there are some examples of badges and key-rings I made. Just use your imagination and DON'T LIMIT YOURSELF.
All of this stuff, you can get in one haberdashery and won't cost you a lot of money.
This is about it. Of course you can use other materials such as leather or beads. You can buy books with instructions for several leather bracelets. Beads look very good too if they are knitted to the bracelets itself. Imagination doesn't have limits, and everyone can make whatever they like. Furthermore, you can use different fastenings on the end of bracelets.