I did this for Bare about a year ago. When I got to the C-store there were over 2 dozen cooler doors with 50-100 product facings each, plus a couple of smaller ones scattered around.
I took pics of the facings. It took at least 2 pics per door so that I could read the product labels, including sizes, later. You have to enter every product separately. Not just "coke" - there is 12 oz coke, 16 oz coke, 24 oz coke, are they cans, are they bottles, etc. I had to go through every picture to get the final count for each product. Entering all that into Excel took quite a while.
Then there were several follow up emails from the editor to clarify things. I swore never again.
As always, your milage may vary.