At a guess, people would pay their rates, taxes and any associated fees the government sets for the public. These fees might probably be a week's ages (or higher) requiring a person to make a one off purchase of bitcoin to enable them to make the transaction.
As others then go onto say Lightning Network transaction fees are enabling entry level users to make micro payments (i.e. McDonald's/Burger King etc as we reported in another thread) for small value transactions.
The Federal Government might be stockpiling it's initial purchase to both instill confidence in the citizenry and also as a replacement to a more traditional store of wealth e.g. Gold in Fort Knox.
There are also other places that does it off-chain as well. Think of it like having a paypal, all of the money is there anyway, and then you work your life regularly, and then instead of people paying you fiat to your bank account, they pay you bitcoin to your wallet, and it is in their wallet as well, and the nation as a whole just moves money from one wallet to another on that app.
This way the app doesn't actually do crypto transactions, it just moves money from one account to another account for a very small fee. Sure the first entry is the big one but companies of that nation probably doesn't care about the small entry fee when they have so many workers, or the shop owners do not care about the first entry neither considering they will make that back if they are good at their business. Long story short instead of just bitcoin wallet to bitcoin wallet transaction fee, it is account to account in some app.