I wouldn’t make it. I’d be dead within a year.
I’m a little confused on the premise of the OP.
If we’re talking about a situation simliar to a movie premise, e.g. The Bourne Identity—but without the intrigue—I’d go to the ER and ask to be admitted to the psych ward. I’m clean, my clothes are okay, I’m obviously not a bum; yet I have no identity, no collect calls I can make, nuthin’. What explanation is there other than some sort of amnesia?
If it’s not amnesia, but I’m somehow forbidden from contacting friends or family, then I guess I don’t know. I cannot imagine the situation, quite frankly. I suppose going to a sanctuary or church, for example, for help. I’m literate, well spoken, and educated; be honest and sincere and ask for a break. As for getting an I.D., I know how to do that, but it’s illegal. I assume that getting my own I.D. back would be proscribed in the same sense that I cannot contact friends & family. So creating a new identity is doable, if not risk-free.
First thing (aside from basic survival necessities) would be I.D. I have no idea how that works if you have no current forms of I.D. and one to vouch for you, but there must be some mechanism. So I’d go to a police station and ask them what to do. Presumably, I’d be a ward of the state while this gets sorted out.
Once I had the identification problem solved, I’d need some money and a place to sleep/bathe. I’d spend my time begging for money and a job. Something along the lines of what Annie-Xmas wound up doing, I suppose. I’m well-spoken and clearly not deranged, so I imagine I could find some job on the lowest rung of the ladder.
Once I had a way to make a tiny bit of money and keep myself from looking like a bum, I’d play poker. It’s what I’m (sort of) doing anyway right now, and I know I could make a decent enough living at it. Finding a live game might be tough in most cities, but I could always move to California (or Vegas), where card clubs are legal. Anyway, once I had a checking account and enough money to fund an online poker bankroll, I could make it as a respectable citizen.
Start a life of crime.
Not the best way to live, but I hear it’s done quite a bit.
Um, any step-by-step instructions on how to do this even if one is not abandoned in a city with nothing? Say one is already somewhat established (employed, house, Social Security card, etc.), but wishes to marry rich. How, exactly would one go about this?
Just curious, of course.
And 3 days later, you’d be out on the streets again in a drug-induced haze and in exactly the same dire situation as you were in when you asked to be admitted (if you were lucky). 
I think I’d “seize the day”. Without access to any of my job history or educational records, etc., I’d have a tough time getting a worthwile job. I’d panhandle until I had enough to afford a backpack and other minimal camping gear, and then spend the rest of my life wandering semi-naked through a national park, without any immediate concerns other then finding some food and shelter for the night.
I fantasize about doing that now, if I found myself in the situation described in the OP I’d have no excuse not to.
I knew a guy who hiked the Apalachian Trail. One thing he learned is that what you’re describing just won’t work. You’ll starve in the woods with no money and no one to turn to.
Also, I’m not exactly sure what size a medium-sized American city is, but I question the idea that panhandling is a stepping stone to great success.
I’d contest your friend’s claim; the ability to survive “off the land” depends upon a set of knowledge and skills that most hikers do not have.
If you’re on the move, trying to make you 30 km/day then there’s no way you are going to forage well enough to feed yourself, espeically with the 3000+ kcal/day requirements. On the other hand, if you are skilled enough to identify nontraditional food sources, set snares, and build fish traps, you can eat quite well in the woods, at least, during the spring, summer, and fall. Of course, you are going to be spending the bulk of your time, initially, building and placing snares and locating food sources (plus building shelter and other necessities) but once you’ve got a pattern down you can survive quite well. This is assuming, of course, that you are left alone, unmolested by authorities, and that you are not in competition with many others for the resources; living off the land after the fall of civilization, with the countless masses all shooting after the same bedraggled squirrel isn’t going to leave you with good odds.
Stranger
Identity theft. Preferably Donald Trump’s.