Technically there are two things here, but since they are both erasers I'm counting them as one! I discovered the Moo Eraser a couple of years ago at the Florida Watercolor Society Convention. What is so special about it you might ask? I've actually been able to erase pencil marks off of my watercolor paper after I have put paint down. No other eraser I have used does this without destroying the surface of the paper. They are very gentle on the paper surface and don't create a lot of small crumbs. I also use it while I'm drawing my image on the paper if I need to erase. I can cut them in small pieces to get sharp edges and corners. They are kind of hard to find but when I find them I stock up. It's the only eraser I pretty much use for everything except for a kneaded eraser occasionally.
You might ask what on God's green earth is the knitted puffy thing. I have been using the Alvin Dry Cleaning pad as a designer, since I started drafting back in the.... well let's just say back in the day before computers and everything was hand drafted. It's a knitted bag full of small eraser crumbs that when you squeeze out deposits them on your paper. When drafting it removes the extra graphite on your vellum that can cloud up blue prints. (OK now I'm really dating myself.) I use it now to lighten the graphite if it's gotten to heavy after I draw my image on my watercolor paper. Just squeeze out a small amount of crumbs on your paper and then rub the pad lightly over the drawing. Another indispensable tool at this point is a drafting brush. That's a freebie so there really will be 11 favorite things.
Drafting Brush