I'm in the US, but I've seen plenty of plastic egg cartons. Most are paper, but plastic isn't uncommon in my experience.

Completely forgot that you guys have literal milk bags. lol

Packaged together in another plastic bag, then placed in yet another plastic bag at checkout. It is the Russian doll of consumer packaging.

Avalon Dairy in BC uses glass bottles, and grocery stores which sell them take them (in exchange for your $1 deposit) and send the bottles straight back to Avalon. They get cleaned and reused directly. If you're at the store, you can look closely at all the bottles and find the dates they were first used. Alas, I've kind of gone off getting them now that we're using 2L bottles of milk every week - the bigger bottles are extra bulky and my nearest grocery store doesn't sell Avalon.

I'm still a big fan, though. It's a good system, it genuinely causes the bottles to be reused (instead of just not made out of plastic, or "recycled"), and it's so simple. We could easily have this for everything if we regulated (or at least incentivized) specific containers for groceries, at least for things packaged domestically. No more needlessly complicated special jars for different brands of maple syrup. If every company used the same containers, when they reach the recycling depot (hopefully intact, although that's another problem) we could actually do something sensible with the things.