If possible, try to have some water near. Drinking a bit of water helps me when the hardest part is over.

Same if the person has anything that can help (I have no meds so idk in such cases), plushies or whatever.

But don't leave the person alone without asking them first. Sometimes someone that take care of us when the panic attack is here is more important than anything else. Ask, always.

Also I for myself have a really hard time with my hands and fingers when panicking. I have troubles for holding anything simple or taking a tissue, etc.

So do things slowly. Hold the glass of water until the person holds it well and say its ok.