I believe we already have the resources to colonise the Moon and maybe Mars right now. There would have to be considerable R&D, and willpower, and it would be very expensive but I think it is within our powers. Humans would have to live underground and deal with dust, maybe microbes in the case of Mars, but we could do it. The spaceships to go to Mars would have to be big but they could more easily be built on the Moon due to the lower gravity.
It's easy if you can build some kind of machine like what Eric Drexler talked about that could manufacture absolutely everything. Otherwise it's impossible.
The best hope for that is to send the one thing to Mars that people absolutely refuse to send to Mars which is bacteria and yeast and microbes. That could be a synthetic biology platform that could make pretty much all the molecules you need and then you assemble them with 3D printing or something like that.
> I believe we already have the resources to colonise the Moon and maybe Mars right now.
That is or was essentially the mission of the US government's Artemis program, as I understand it. Some elements of the plan are (or were):
'Civilize' (my word) the Moon - build PNT, situational awareness, communication infrastructure, bases, permanent human presence etc. Bring it within a normalized region of operations, like Earth orbit (though obviously much more expensive and less utilized). A benefit is developing plans for infrastructure and operations on Mars, in a much more friendly and less expensive environment. What does it take to support humans efficiently and reliably on another body?
Also conduct experiments and develop technology for Mars in cislunar regions - again, much friendlier and less costly.