I've been a proponent of a living wage myself, but there is one glaring problem with the model I propose: it would require another local level of beaurocracy in every community - i.e. more taxes and more government.
Basically, every town would require a 'department of living standards' whose function it would be to keep track of the essentials, in order to regularly adjust the living wage. I don't think the wage could be adjusted in less than a year's time adequately; quite possibly, adjustments would be rather ad-hoc from year to year. Oh, sure, it would be simple to assign one person the task of food price evaluation, another the task of living quarters evaluation, and so forth; but we all know how local government agencies actually operate. It's usually one person doing the job of ten, swamped with unnecessary bookkeeping and paperwork, and hampered by regulations from every quarter.
As to what should be in a living wage: in my opinion, a single person working a full-time job should earn enough to pay for rent at the lowest cost property that meets health and safety regulations; adequate food to maintain good nutrition at the lowest cost of a menu designed to make well-balanced, nutritious meals; electricity for a household operating basic equipment; heating and cooling costs; transportation (this could be no more than bus fare for cities with buses, up to the cost of fuel to travel from one end of the city to another); basic medical needs (assuming the person is on public medical insurance); an allotment for personal non-food needs (hygeine essentials, etc.); and a percent that covers taxation and fees that a person is required to pay (for example, water bills, residential tax, garbage, etc.)
This living wage would be just that - not enough to buy luxury items, pay for entertainment, splurge on fancy dinners or eating out, buying cars, etc. Those things should be available as one earns a greater-than-living wage, either by gaining better jobs, getting promotions, working two jobs, etc.
So for my notional agency, I think you'd need a nutritionist (at least one at the national level to write policy on what constitutes a reasonable menu), someone to determine standards for safe and healthy living environments (again, at a national level at least), an energy analyst to determine what kind of electrical/gas use is acceptable, transportation experts who can determine the lowest cost of transporting someone to and from work (not counting walking), and other experts as needed by region. You'd need a staff that works the local stores to determine costs for basic food items from the menu, a staff that visits and monitors rental properties and available housing, a staff that keeps track of energy costs and other fees and taxes, and so forth.
A minimum living wage should NOT take into account people living at home, people being fed by their families, people driving (though, in some areas, no other method of transportation is available, and driving should be considered then), carpooling, people living 'off the grid' (generators, wells, small farms), and so forth.
If you work in a job full-time, even at minimum wage, you should be able to survive by yourself. Too many people have the attitude that minimum wage jobs are only for teenagers living at home with mom and dad. Look at any min-wage job, and you'll see a LOT of other people - adults, people with families, etc - trying to make it on these jobs.
I also don't think families should be taken into account with living-wage jobs. The family isn't working the job; the individual is. Enforcing such a standard might be another incentive for people to wait before starting families until they've surpassed the living-wage income level.
But as I said above, in order to implement and enforce a living wage, we'd have to add yet another tax-funded beaurocratic level. Sure, this means more jobs nationwide; it also means more costs nationwide. And unless they're going to try to project costs, every living wage increase would be at least a few months, if not a year or more, behind the actual living wage. Working with cost projections is tricky, as costs sometimes exceed projections, and sometimes lag; the living wage would be a hard target to hit.
One possible method to counter this would be to make the living wage sustenance plus a percent, but again, that percent might not always match actual cost increases. It might also exceed actual cost increases, and the motivation here is to match wages to expenses as closely as possible.
Another problem I see in this is that the lowest-available costs aren't always going to be available. If the lowest-cost rental in town is $400 a month, but only two units are available, and the next lowest-cost rental is $1000 a month, setting the rental wage at $400 is going to leave all but two people far behind on being able to meet their bills. One possible angle to work on this is to also have a staff whose function it is to determine how many employees are at living-wage level in their area, so as to determine the lowest cost at which all living-wage earners can gain housing; again, though, this is more difficulty to add into an already difficult system, and doesn't take into account those who already possess lower-cost housing.
Plus, the entire system would be subject to the whims of the politicians, who would undoubtably push their own agendas. Liberals would want entertainment or spiritual considerations added into the wage, or would push for an increase for 'morality-boosting' activities; conservatives would demand that measured costs were deliberately being padded or that we should exclude housing because we already have welfare-based housing in place, etc.
IMO, welfare shouldn't be included, because the goal should be to get everyone off of welfare, if possible; but that's unrealistic, and I know it.
If we could remove politicians from the picture, I'm positive that, with some effort and a large expenditure of taxpayer money, we could come up with a working system to maintain living wages; but that's never going to happen.
So as much as I'm for a living wage, I'm also quite aware that it's not a feasible idea.