Every. Single. One.
I'll talk about that in a moment, but first why that is so? Expense. There is no way to get around the fact that establishing our first settlements in space is going to cost billions of dollars. Most people don't have a clue about how to get around that and partly it's because they hold so dearly to this nutty idea.
The other fact is that survival is going to be hard. So, reinforced by this nutty idea that has been shown to never work for long, ever in history, though it's been tried many times; they make elaborate plans to cover every detail. This is the central planning fallacy. In small doses it's not too bad, but when it reinforces the human tendency to want to control others it's a problem. A big, huge problem.
The nutty idea is that space is so hard and so expensive that you can't allow liberty to stand in the way of a great plan. So they come up with central planning strategies to control every minute of the activities of potential colonists making them slaves (but they would never call them that.)
But liberty works. Ownership works. We should give it a chance. It's also the only way I know of to get around the fact that establishing a settlement is going to be expensive. Ownership totally and completely pays that entire expense! Today. At current high costs. Nobody else has a plan that does that and gives freedom to settlers. The Space Settlement Initiative does the former but not the latter, essentially creating a company town. We know about company towns, they have a history (and a great Sean Connery movie.)
People like to control things they have no right to. Space is full of unclaimed territory. Nobody owns it. All unclaimed territory becomes owned by somebody when they make the first claim. People assume this claim has to be made by a sovereign. This is a false assumption. Anybody can claim something that doesn't belong to someone else. All of space is not owned by someone else. It doesn't matter what lawyers on earth argue or treaties nations sign. People are not slaves even if they act like it. If a group of people get together and agree to establish an orderly way to make claims... It has the force of law. Once claimed, property is bought and sold, conveyed by deed, and has a chain of title like any other.
It's the only known way to pay for space settlement that can start now (because it doesn't require some outside agency to give it's blessing. To counter those that would like to regulate that which they have no right; claims do not have to be made public until the time is right.) We don't have to wait. Can it really fund the billions needed to start a settlement? Yes. Here's how...
I propose the company that agree to deliver settlers to a colony according to the terms of a settlement charter get to claim 1000 sq. km. as their own for each colonist they transport (free for the colonist including a metric ton of supplies. Skinny people get a bit more supplies. Life just isn't fair to us fat guys. The supplies the colonist pays for, the transportation cost is paid by the company.) So if the first mission to mars has a dozen colonist (in two ships, I suggest) they would be able to claim 12,000 sq. km. as part of the terms of agreement to a settlement charter. But that land is worthless isn't it? Yes, that's close enough to true. It has very little value to start. What will make it valuable will be settlement itself. BTW, the more colonists they transport per mission the lower the cost per colonist and the more potential money the transportation company will make. It also means more colonist to support each other giving the new colony a better chance of survival. Sending less than a half dozen at first is nuts because it doesn't do much to establish a new colony. Do you imagine six people could have made a viable go of north America?
Developed land has value. It will take settlers to develop the land and give it value. Robots could do some of that (if you want to wait forever) but even robots can ultimately not give the land value. Settlement gives the land value. So in the above scenario we have a company owning 12,000 sq. km or 1.2 million hectares. It will take time to give that land value and only settlers will do that (we aren't going to mine anything on mars that will be worth transporting back to earth.) So pick a number for how much it costs to deliver a dozen settlers to mars? Now divide that by 1.2 million. That's how much is needed on the sale of a developed hectare (about 2.47 acres) to cover the cost of delivering those colonists. If your plots are about a typical half acre then divide by 6 million instead. That transportation company isn't going to recover their costs immediately. But they don't have to and may even have other means of covering their costs. The important point is as they add colonists that land will go up in value many times more than the cost of transporting the colonists and supplies. The land near the colony will go up in value first. The land farther away will go up in value later.
I say I can put a dozen colonists on mars for much less than $6b meaning the transportation company needs less than $2000 an acre to completely cover their costs. At some point down the road development of that land will make it worth much, much more. If Elon is even close to right that he can bring transportation costs down to $500k per person this brings the recovery cost down to $10 an acre. Do you suppose some people that will never leave earth might buy a few acres? I do and that's undeveloped property. Before any real value has been put into it. As a matter of fact, the first settlers will probably be the first buyers as well. That's because the settlement charter limits their claim to a single sq. km. But they are going to realize that the value of land is going to go up as more settlers arrive. So many of the early settlers are going to buy more land. The transportation company may sell that land cheap to early settlers before the value goes up, perhaps for $100 per hectare ($10,000 per sq. km.) ...or $370 for 32,000 sq. meters (you'll have to read other posts to discover why I picked that area.)
This plan, zero transportation cost per colonist today, even beats Elon's $500k per person sometime in the future (if ever.) Which means the colonist can concentrate on what they are going to bring (which must include the proper life support for about a six month trip and the first few years on mars. Mostly freeze dried food.) Much of which will depend on the recycling capacity of the transport ship and what is available once on mars. Each colonist will then have the liberty to bring the tools they have the skills to use (within the weight restrictions.) Space suits are obviously going to have to come way down in cost.