Crossword Genius

A mini Tesco mistakenly knocking point off bill for bag for life (8,3)

Ross

I believe the answer is:

amniotic sac

I'm a little stuck... Click here to teach me more about this clue!

'a mini tesco mistakenly knocking point off bill' is the definition.
I know nothing about this answer so I can't judge whether this works.

'bag for life' is the wordplay.
I cannot really understand how this works, but
'bag' could be 'sac' (a small bag) and 'sac' is located in the answer.
The remaining letters 'amniotic' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...

'for' acts as a link.

Can you help me to learn more?

I've seen this clue in The Independent.
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