The context of the word "bag" in KJV John 13:29:
KJV John 13:29, For some of them thought, because Judas had the bag, that Jesus had said unto him, Buy those things that we have need of against the feast; or, that he should give something to the poor.
The word "bag" In KJV John 13:29 translates in context to mean a "money box" as my translation notes say in my King James Version (KJV) Holy Bible.
The word "against" in KJV John 13:29 means "for".
Lastly the context of the word "sop" in KJV John 13:30.
KJV John 13:30, He then having received the sop went immediately out: and it was night.
The word "sop" in KJV John 13:30 according to my King James Version (KJV) Holy Bible translation notes means a "piece of bread".