You will need to draw out the 4 x 4 grid shown on the link and then add in the missing numbers. You will know that you have got it right when all of the rows and columns add up to 34. There is only one way of doing this, so it may just take a little time.

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Once you have that, then each item on the grid will have a number assigned to it.

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You then use the shopping list to identify the items on the grid that you need to use. Each item on the shopping list has a commonly associated item, for example salt and pepper. As pepper is on the list, the missing item is Salt. The salt shaker is on the grid square with the number 9. The 9th letter of the alphabet is i.

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Repeat this for the other items on the shopping list. The items are listed in the correct order to spell the password.