A lot depends on the exact context of the conversation, but this is what it could mean.. "You wanna go get some?" --- Do you want to go (with me) and get some X ? "You wanna go get us some?" --- Can you go (without me) and get us some X ? X is something already known through the context of the conversation... ---- e.g. Person A: I'm going out to get some coffee. You wanna go get some? Person B: Sure, Lets go. -- Person A : I'm so hungry. I could really go for some pizza right about now.. Person B : Me too. Person A : You wanna go get us some? Person B : Okay, which one do you want?

もっとコンテクストが必要あると思います。　たとえば、何をとりにいく？ ”You wanna go get us some　＿＿＿?" ”なんかをとりにいかない？” Hope that helps!