Supplies for fashion design. There are so many supplies out there that you could choose from. The best way to go about it is to systematically try different things.
You need your mechanical pencils. They're very important. Different level leads, as far as hardness is concerned. You need to have a beautiful pen that you feel really comfortable drawing with.
From there you could start to explore how you're going to color in your fashion illustrations. Whether you want to use pastels. Whether you want to use watercolor, gouache. Whether you want to use colored pencils. I can go, there's many other mediums out there. But, what's most important is to find a medium that you're most comfortable with. And to work with it to the best of your ability.
There's all sorts of other tools that you're gonna need. You're gonna need a good smudger, good smudging stick. It's how you create all your shading. You're going to need a great eraser. Because, lord knows, you're gonna make mistakes. And that doesn't matter, you can just erase it. White out is a great tool for finishing sketches. There's all sorts of things.
Just really have fun with it and really get comfortable with using your tools. So play around. Experiment. Play around with different kinds of paper. There's marker paper. There's all sorts of vellums. Etcetera, etcetera. You could even use cheap, printer paper if you want. That's a great thing to just practice on.
So those are pretty much all the supplies you need to create a fashion portfolio.