The biggest issue with alcoholic beverages are the taxes that go along with them. Some countries have very high alcohol taxes while others have almost none. That would seriously throw off the PPP calculation.

It needs to be consistent quality and non imported ideally.

Guiness for example is going to cost a lot to ship, or local beer could be very low quality in order to keep the price affordable.

Or just count the cheapest alcohol available

Again it will likley be imported from countries with lower labor costs.

You need something perishable, and of low enough cost that importing is unlikley.

Bread would be a good option but has the issue that it's not as common in Japan as France, it also varies wildley where as a big mac is generally consistent.

A Big Mac, as a branded item, varies by cultural context: in the US, it's super cheap fast food; in Europe it might be late-night after-party food; in Asia, an extravagant treat.

Yes please, it always helps an economics discussion.