When people call something a public good, they usually refer to things like so-called public roads, public buildings, public schools etc.
But those things are not public. They're state-owned. You need permission to use them and you may even get arrested for trespassing f you try to enter a 'public' building without permission. Calling them public is manipulative statespeak.

So what would it be fair to call public?

One thing is information. As a non-rival good, it's truly public. This includes FOSS, but also any code that has been leaked to the public. Similarly all the books (in the sense of content, not the physical material), scientific knowledge, musical compositions etc. Protocols, like TCP/IP and Bitcoin.
I'd also say the internet, i.e. the network itself, is public. Its infrastructure (cables, servers, routers etc.) is owned by private entities, but the network is a public good. As are natural languages (English, Spanish etc.), programming languages, sports, games like chess, the metric system and so on.

But what about the physical?

It gets tricky, because physical goods tend to be scarce.
One could make an argument that - at least from the perspective of our life on Earth - the sun, the moon and the stars are public goods; they benefit us (by giving us warmth, light or navigation tools), but none of us has any more right to them than anyone else, particularly due to our physical limitations, which don't allow us to access them in ways other than basking in their light or looking at them - at least for all practical reasons and for the time being.
The oceans and the air could also be argued to be public. The same limitations don't exist as in the case of celestial bodies, so their 'publicness' is not guaranteed. However, their public status is owed to a combination of factors: their perceived abundance, difficulty of access, low utility etc.
No one's land, such as the Antarctic, could be viewed as public, but if we find we can e.g. mine bitcoin there using geothermal energy, it will cease to be public in no time.
this territory is moderated
Dang, you really hit on something here. Language can both clarify our understanding of the world and cloud it. The propaganda by and about the state clouds our understanding. I try to replace "public" with government or state when in conversations because as you say these things are not truly public. That is literally a lie we are told over and over. It is beat over our heads so much that most just accept it.
I hadn't really thought about information being public though. I think I agree. When you go down the trail of thought about what is private and what is not you will get to property. You get to who controls a property vs. who supposedly owns it. Control is where its at. I can think I own something but if I can't control it do I truly own it?
You can't really control information once it leaves your mind. Information is not scarce. It is not tangible. States and Kings have created a construct. A lie called intellectual property. We know it isn't really property because they had to add the world intellectual in front. So they at least admit it is different from what we have understood property to be for thousands of years.
The idea that you can own an idea, a word, a song, a line of code, or a recipe is ridiculous on its face. Its a construct backed by the threat of violence. That's all IP is. Information is public. Its truly public in that as soon as it is shared you no longer control it. Bitcoin is public. It was private before Satoshi wrote down his ideas.
Thanks for giving me a new angle to think about these things.
You're welcome, but these ideas are not really that new.
Yes, IP rights contradict normal property rights. If I own a printed copy of a book, I'm free to do whatever I want with it; in particular, to read it aloud in front of an audience or copy it. If I obtained the book under the condition I wouldn't reproduce it, and signed a contract, that's a different story though - because I'd be breaching the contract. But once I've done it and shared as e.g. as a torrent, those who download it can do whatever they want with it, because they're not bound by a contract. The unenforceability of such contracts in some common scenarios is yet another story...
Yep. In a world where taxation is not considered theft the meanings of words are suspect.
Nice scenery is sometimes considered a public good. States occasionally seize on that argument to prevent development of private goods that would disrupt the scenic view.
Another physical one, that builds off your initial argument about the roads (When are they going to finish those damn roads anyway?) is paths or trails. Unlike roads, paths and trails are often formed by repeated use of particular routes, rather than being constructed by a particular person or entity. They were essentially homesteaded by the members of the community that formed them and as such are owned in common by the public. As long as traffic remains at a stable level below congestion, they are also functionally non-rival in their use.
Both valid points.
Yes, paths and trails are public, as long as the land the go through can be considered public within the scope of the paths' use (which is to walk on it, and not to, say, build a factory or dump trash on it).
The analogy of celestial bodies as public goods hit home
so-called public roads
travelling on "public" roads is a right, if you know to use it
public building
State owned should be tax payer owned.
Taxpayers own but managed by state or city or county etc
I disagree. These are public goods because you use them without contributing anything to their development. You didn’t buy the materials and hire the labor to make the road the government did. And this idea of permitting is to prevent people who don’t know what they are doing from killing everyone who does. You don’t get asked by the government every day to drive on the road. Once you pass the test you can drive on any road in America with little to no problem. Thus making it a public good.
FOSS is a public good but even in bitcoin they have gatekeepers who maintain the bitcoin protocol we all run on our nodes. You can argue how they ship new versions of core is a quasi government. From the BIPs and everything that is associated with the protocol.
This anti state stuff is laughable as people sit comfortably from their well lit homes with a full belly of food and yet think the government is the root of all modern problems. I beg to differ. Is the government a major problem absolutely but let’s not make it seem they don’t do some good as well. Bitcoin wouldn’t exist if it wasn’t for the state because the state created sha-256 cryptology which is what bitcoin is based upon.