In an ideal world, everyone would be able to meet their needs without resorting to use of non-renewable resources. The easiest way to do this would be to use the free services of their local ecosystems. When populations can't do this, they have several options: They can find a way to live on less, grow the ecosystem, expand their territory, move, or trade something they don't need for what they need.
Living with less can be done by changing choices of food and materials (to get more utility out of a part of the ecosystem that is more plentiful than others), using more efficient methods (such as building smarter or preparing food differently to get more nutrition out of foods), and developing technology that can get more use out of both the ecosystem's resources and human labor.
Growing the ecosystem is another way of saying “increasing its biocapacity,” where biocapacity is the annual ability of the biosphere to provide what we use and clean up what we waste. This could involve importing more (preferably native) species, reducing pollution, and changing the landscape to be more conducive to life (such as growing or importing soil, capturing and routing water, and adding weather protection).
Expanding territory and moving are the easiest ways to get what you need if your ecosystem can't provide it. There may however be physical impediments (places you can't travel) or human ones (other populations already living where you want to move). An efficient way to do this is to provide incentive to a small part of your population to take the risks for you by giving them or promising them more than they need (paid for by having the rest of the population live with less), then moving or expanding the rest of the population when a satisfactory environment has been found and the means for accessing it developed.
If other populations occupy ecosystems with sufficient additional biocapacity to help yours meet its needs, then trade may be an option. What you would trade is resources that you don't need, but which the other population wants. Because there is also risk involved in making such transactions (both in determining what can be traded as well as performing the trade itself), a small set of risk-takers can also be employed by one or both populations.
Now, trade connects practically every population on the planet. Encouraged by the incentives of risk-taking to use more than they need, almost everyone is joining the ranks of the risk takers. This has created a global culture of growth, with disastrous consequences.
According to the recently released Living Planet Report by the World Wildlife Fund, our global population exceeded the ecological carrying capacity of the Earth (the biocapacity needed to provide what we use and waste) by half in 2007. This means that if we relied strictly on biocapacity, only two thirds of our population would have been able to sustain its annual resource use and waste (“ecological footprint”). We've made up the difference by “consuming” the very species and systems that do that work. For reference, the report comes up with a minimum healthy, sustainable per-capita ecological footprint (for Peru) that is roughly half of what the world is probably using now if per-capita consumption is still proportional to population. If biocapacity stays constant and the average per-capita consumption drops to this minimum, then our planet will sustainably support no more than eight billion people. (This, interestingly, is very close to the peak population my own population-consumption model projects for business-as-usual with no renewable resources.) The global population is approaching seven billion people; if we all lived like people in Peru, I estimate we would be using seven-eighths of the world's carrying capacity.
If we could somehow manage to redistribute the world's population so everyone could meet their needs using the available biocapacity, grow biocapacity, and limit whatever extra we consume (meeting our wants) to the added biocapacity, then we would probably have the best of all worlds. With more self-discipline, we could set aside a reserve as a cushion against external forces that might reduce what we have (such as global warming, which is almost sure to have this effect).
Implementing this admittedly simplistic plan would seem to require centralizing the population rather than splitting it up (as I've suggested in the past), but this isn't necessarily true. A thorough analysis could theoretically be done to determine the optimal distribution of population on the planet given local biocapacities, energy resources, and projected changes in the environment on both local and planetary scales. The analysis would have to consider how to reduce the vulnerability of connected populations to threats that could imperil them all, which I believe will result in suggesting some degree of isolation.
Far more difficult than coming up with a physically plausible “ideal world” will be convincing the vast majority of people who subscribe to an entirely divergent set of cultural norms and beliefs that it should be followed at all, and then changing their way of life to accommodate it.