This scarf is knit with two types of yarn. The first can be any weight of yarn, but the second needs to be a light weight that will not change the gauge by much. This scarf is suggested to be knit with the largest or next size up needle suggested on the ball band of the thicker weighted yarn.
Yardage needed is for your desired length, but with Bulky size weight anywhere between 240 and 260 yards will be long enough for the main yarn. You will need close to 50 yards for the light weight yarn (again, yardage may very depending on gauge of main yarn).
An added flair for the scarf:
If your light weight is a sparkly novelty, or something contrasting rather than complimentary to the main yarn, it will give a little pop to the pattern.