I know someone who lost their ID and is having trouble getting it replaced due to not having the right paperwork available. Based on his experience, it is very hard to get by without ID. You need it for everything nowadays.
However, he did just get a bus ticket by using a secret answer to be able to pick up the ticket.
In this scenario, I am assuming an NYC resident would have some money in the bank, and could max out their credit cards with cash advances, so they should be able to raise $3-5000 in cash. Given this, you could buy any gear you need at a Walmart, if you don't already have a go bag.
You could buy an untraceable prepaid MasterCard or Visa and put part of your cash on it, so you could pay for things online when needed. Likewise you can get a phone with a phone card and it would be untraceable.
So, you could get cash, travel gear, usable credit card, phone, and bus ticket. However, you could not rent a car or a hotel without ID.
You could wash up in a bathroom with a washcloth and a bar of soap. Truckstops sometimes have showers, and so do gyms, but I think you'd need ID to get a temporary pass at a gym, and the truckstop might not be accessible if you don't have a car.
You'd want to get to Mexico as fast as possible by bus, but possibly lay low a few days first as mentioned. It might be hard to lay low in NYC due to the expense and the difficulty of finding shelter without using ID. I would not trust friends, unless you explicitly have that level of trust. You can't know how they will react when an apparently credible source says you are a murderer.
Once you realize you're headed to mexico, you'd want to start cramming to learn Spanish (and then Portuguese) . You'd have a couple of days on the bus ride to think of a cover story and detailed fake back story, then use them in Mexico to make your way to Brazil.
I agree that seducing fat girls would be helpful. I don't recommend MikeCF's plan for becoming a gay gigalo!