That's how you get weird things like the AI determining that your favorite items are jam, baking soda and whatever you left at the back of your fridge to rot for six months.

It is easy to detect what's in your fridge. We have that today on some smart fridges.

The problem to be solved though is

• what's in your fridge
• what's not in your fridge
• what do you consume vs throw away
• what do you buy
• where do you shop
• what prices are available
• what's the best way to minimize cost and store trips
• what's your metric for how to balance that

Of those things, AI is really only helpful for determining the metric for how much money you need to save to add another grocery stop, and knowing that the orange blob is probably baking soda.

Most of the rest of that is manual inputs or relatively basic but tedious programming, and those are the parts that would be the most annoying.
I say this as a person who has repeatedly utterly failed to use https://grocy.info/ because actually recording what you eat vs throw away is painful.

This isn't a great AI problem not because AI can't help, but because the tedious part isn't the part it can help with right now.

Probably would make sense to start with the receipts for what you purchase and aggregate lists from there (pantry, freezer, fridge, etc.).

Yeah, kinda. Except you'll likely need a camera or two for each shelf of the fridge (given the layout remains unchanged), and also you have to make sure they don't get covered with ice/spilled milk/whatever or blocked by a box of some stuff. Aaaalternatively, you install a receipt scanner and touch scrreen which asks you what you took and updates an internal db accordingly.

then I feel like cameras to detect what's in your fridge is pathetically easy in comparison

But you're skipping over a huge amount of context that's missing. It's context we (as humans) take for granted. What's the difference between a jar and a bottle? Is the cream cheese in a tub or in a little cardboard container? Then it would need to be able to see all items in a fridge, know the expiration dates for each thing, know what you want to get, how quickly something gets used, etc.

Some of those things are more straightforward, and some of them need data well beyond "this container has milk". The issue isn't processing all the data, but acquiring it consistently and reliably. We humans are very chaotic with how we do stuff in the physical world. Even the most organized person would throw off an AI system every so often. It's the reason self driving cars are not a reality yet and won't be for a while.