YOU SAID:
I'm going to the sandwich shop to pick up some biscuits
INTO JAPANESE
サンドイッチ店に行ってビスケットを買いに行きます
BACK INTO ENGLISH
I go to a sandwich shop to buy biscuits
INTO JAPANESE
私はビスケットを買うためにサンドイッチ店に行きます
BACK INTO ENGLISH
I go to a sandwich shop to buy biscuits
You've done this before, haven't you.