Translation for “as it is”
Chinese does not have a exact translation of そのままで (其の儘で) which is as flexible as the situation that you've described. The literal translations are


照原樣
依舊


which both mean something like in accord with its original nature/form, but we would not use those terms to decline a shopping bag. Instead, you may say something similar to the following in casual vernacular:


不用了 (No need)
這樣就行了 (It'll be fine like this)


(2) matches そのままで fairly well in meaning in this case.