Along with the question @Jeruba referred to, there was a question in a similar vein about “What should I do if I’m about to be homeless in [Seattle or the Pacific Northwest, I think]?” from a couple or three years ago. (I only recall that because I participated in it, but I can’t find it right now.)
Since that’s what this is about, not so much “survival”, but “how can I improve my situation”, it puts things in a different light.
The first things to do if you’re homeless are to find some kind of secure (relatively) and dry shelter. You can get warm later if you’re dry, but if you’re wet in the cold then you’ll have a hell of a time getting warm. And if you can’t stay warm then you’ll die. So, in order of importance:
– find some place to sleep / stay / rest that has some marginal security;
– be sure it’s a dry place (and keep in mind that a place that is dry “now” may not be later if the weather turns);
– after you’re secure and dry is the time to work on staying warm;
– when you’ve arranged some kind of shelter then you will need a source of fresh, potable water;
– if you’re in a non-urban and arid area, this may be the most important thing, so you need to be aware of where you are and what resources you have; obtaining drinking water in an urban, industrialized area with nominal sanitation is normally not a tough thing to resolve – you can always resort to finishing half-filled bottles of drinking water discarded every day by those who can’t be bothered to finish them or carry them any longer; it’s not ideal, but if someone else was drinking it, then you probably can, too;
– find a way to feed yourself, which can range from dumpster diving to simply asking people to buy you a burger outside of a restaurant; people are much more likely to “actually feed” someone in obvious need than they are to give him money for who-knows-what purpose;
– depending on the weather, the condition of my feet and the ground I have to walk upon, obtaining shoes or sandals would be a low-priority item; in very hot or cold weather or very rough or dangerous terrain then foot protection would be a much higher priority; the homeless have to be mobile (hence the term “vagabond”);
– part of the issue of “obtaining security” (and sometimes unexpected help) is letting yourself be known to the police; if they know that you’re intelligent, sane, more or less polite and non-threatening, then they will not only not hassle you (usually) but may go out of their way to assist you in obtaining the other things you need – even temporary labor or direct assistance.
So one thing that I would counsel is to simply be a bit outgoing: friendly, helpful (just standing in one place, smiling and chatting to passers-by and opening a door to a public building could start a valuable conversation) and letting it be known that you’re not a threat AND that you have nothing but don’t want to steal anything, either. A smile and a kind word can get you a lot. It also doesn’t hurt to ask for “help” more than money: “Do you know where a guy could get some work for the day?” for example. In a suburban setting you could go door to door offering to wash cars, rake leaves or even clean pools for a few bucks. In a rural setting, there is always something to be done, if anyone is observant enough to see what it might be and who might want that done.
I’ve never slept in a garage before, but I’ve slept in my car plenty of times. Secure, dry and warm; it makes my top requirements. (I’ve never slept under a snow drift or a pile of leaves before, but I did sleep under a lean-to shanty one rainy night. I’d prefer the snow, I think.)