I missed "kobieta" at the end of this sentence
If you really wanted to say that, "woman" has to take Vocative: "kobieto".
What is the difference in meaning between "zrób mi kanapkę" and "rób mi kanapkę"?
Besides what mihxal said, „zrób” is more polite, although still casual.
"Zrób" expresses that you want the sandwich to be done for you, whereas "rób" means that you want the sandwich to be being done for you.
Hm... that doesn't make any sense to me. In what scenario would someone say, "Be making me a sandwich"?
You could say so in Polish. But it is less polite and it could sound as if you rushed someone: "You should start making me a sandwich and not doing something else".