One reason the national debt is so damn big is that the federal government owns and operates assets that it shouldn't, like Amtrak.
What we need is a sort of eminent domain in reverse, a right vested in the American people to purchase government-owned assets at fair market prices. If the government wants to put a road through your property, or thinks a corporation would do more for the economy than you're doing, it can force you to sell it. Why can't We the People do the same for government assets? I'd exempt military bases and national parks but everything else should be on the table, especially businesses like Amtrak.
This would force the government to run their business interest profitably or lose them to the highest bidder. The proceeds of sales should be used to pay down the debt; the subsidies saved in future years will of course reduce the budget deficit.