In a nanotech future, you have assemblers which can pull together atoms and make things.
Anything that you have a pattern for, and the correct atoms, can be made. You could make the solar cells to provide power for your nano-assemblers. You could make food, most food is H,C,N,O with some P,K and some other stuff (Ca, NaCl, etc) - most of which is available from the air and water, and if not from those, you can recycle your waste back into food (since it has all the atoms that fed you last time around).
You can also assemble almost anything else you can make/acquire a design for, and have the atoms for. Want a Ferarri? If you can find an unprotected one, you can disassemble it, and reassemble it with your assembler complex - and now you have a pattern. Plug in some steel, rubber, etc and build yourself a second one. Or 20.
So, once you've got an assembler, all of your physical needs can be taken care of (well, as long as you can pull in water vapor, since you exhale that everytime you breathe).
Why would you go to work? And even if you might go to work, but what if most everyone else decides to make themselves a widescreen, a big couch, and eat potato chips from their infi-bag-o-snacksTM?
If people don't go to work, how does the government collect taxes, without reverting to direct coercion?
There (probably) won't be physical money, as is obvious - counterfeiting will be trivial. And there won't be any Treasury officials to hunt down counterfeiters if you can't pay them. But taxes don't have to use little scraps of paper with ink on them. Can be in-kind, could be hour equivalents, could be anything really - that's part of the question. I guess you could directly market-quote valuable atoms, gold coins might become a thing again.
It was suggested that some things are valuable because of their rarity (eg: Gauguin) - but this would be not the case, because of the ease of counterfeiting. When it would take nanoscopic analysis, which might be able to discern assembler errors... I expect the rare-goods market to implode. And what do you buy a rare item with? Another rare item?
Nanites don't create atoms. You still need source atoms, and until everyone has their own collider, you won't be changing the type of atoms you have. But you can recycle your source atoms that don't float away on the wind, or are carried away by insects... or by other assemblers. Preventing theft of your atoms is a thing, especially if there are no courts and no police (how are you paying for those?) to handle criminals.
AI: No AI. Yes, a lot of people might be working on it, but we'll assume that the current state continues.
Robots: Same. Some are around, but they don't do all the work for you. If you had a factory, you could automate it... but why would you have a factory? Roomba to gather up your spilled atoms and dump them in the bin to be turned into component parts, sure.
Assemblers only put things together on plans, so they don't work inside of organisms (or if they do, they scavenge their atoms from the surrounding structure - OUCH!). If you want to implant them, and a tube of feed atoms, well - now you need a specialist, how're you paying that specialist? Timmy's broken leg also doesn't look the same as Timmy's leg of last year.
We'll also assume that you can't disassemble people and put them back together again, and get all of their memories and personhood back intact. Atoms might be in roughly the same place (assemblers aren't perfect), but the electrical network and state it's in are not recreated, and small errors may have significant outcomes.
Which is why you (probably) can't build custom organisms, nor finely graded DNA. Might have some issues with computer chips at the highest end of the spectrum as well, but those aren't atom-for-atom builds yet.
Intellectual property - requires courts and punishments. I expect that open-source will become relatively huge. Since there will be many more people with free time on their hands, and sharing designs will radically help everyone. Even if you make it for just yourself, you can always offer it up for anyone to use and improve, and gain credit to download their designs (online reputation) - or just for the heck of improving the world. I expect only the very rich will pay for designs. And pirating to be a thing.
Energy - I expect many things to be powered directly by solar or environmental harnessing (wind, rain, tides, etc). Some things require more intense power (see below), but as long as you have enough property, your solar output will handle many / almost all of your needs. You may need to save it up over some time, in order to build your palace, but building some power storage isn't a problem.
Property is the big kicker - and protecting that property is also a large problem. Which is why you might want to have a government. Perhaps government works directly on property taxes? You don't pay taxes, you don't get property protection? But that doesn't help with equal access to the legal system, unless property owners subsidize courts and cops, etc for those who don't own property.
Sanitation doesn't exist - you're doing 100% recycling, or you're giving away valuable property. A lot of other services are defunct as well.
IOW: How do you get a cop to put down his donut and get up off his couch? For a fireman to go down to the station? For a teacher to quit knitting and put up with your brats? Or whatever other civil services that most people want. Heck, even to bother counting the votes?
Infrastructure may require a little more effort than just turning an assembler on (in the early stages), since building a bridge is not the same as making an apple. Will require scaffolding, and support, and ability to not get washed away while constructing itself, require pipelines of mass (a bridge is of non-trivial weight) pumped to massive groupings of assemblers, etc.
And, how do you protect the roads/bridges/etc from becoming the source of someone else's brand new palace? Or turned into food (asphalt is yummy hydrocarbons, remember)? How would you protect people's (and the government's) atoms from theft, if you don't have cops?
- Courts - you want IP laws? To have your neighbor quit booming his music at 3:AM when you're trying to sleep? To decide which heir gets how much of Uncle Ralph's huge pile of gold atoms? To decide when a murderer should be put in prison?
- Prisons - how do you administer a prison and pay the guards? And prevent the walls from being broken down? Yes, you really ease the logistics, since you can put a meal-replicator in the toilet, and no longer pay for sewage.
- Beat Cops (physical violence to people, domestic disturbance, etc)
- Property issues (theft - esp. of your atoms; remember even a scrapyard is owned (and that owner is now rich in atoms), government owns the landfills and public rights of way)
- Roads (how do you get where you want to go, if there aren't public means of egress - if all land is privately owned, what's to stop the owners from putting up walls and preventing you from getting anywhere? If the government owns the roads/access - how do they pay their bills/employees?, and prevent someone from illegally putting up a wall and charging access to get to the sea, or to the market where you can buy some gold atoms?)
- Water supply - people breathe out water vapor, and have to get resupplied. Especially true in deserts, many parts of the country you could probably do rain-capture and be okay.
- Environmental protection - who protects wildlife and plant-life from being rendered down into component atoms? Probably won't have dumping of waste, since most everything will be of some value, somewhere.
- Building codes - otherwise people may try building 20 story palaces made of matchsticks, and opening restaurants at the top, and cry "I didn't know" when they kill their customers.
Companies will want money:
- Network connections - If you want internet and telephony, you're going to have to have some connection, and that connection will need to be protected (and/or rebuilt) when parts of it are disassembled, or when it needs to be maintained (But maintenance will be much easier).
- Power supply - some things require more power, and power will need to be provided. Which probably means burning C, and releasing it into the atmosphere. Rather more costly than it has been, since those are valuable atoms being distributed.