Depends on your race and what country you're going to.
If you're chinese or korean, don't go to japan as an illegal immigrant. Actually, Japan is a very hard country to become an immigrant of, illegal or otherwise. If you're not part of a community, forget it.
If you're white, you're treated like royalty almost everywhere. Well, not really. Keep your head down, don't set up a meth lab, smuggling ring, or prostitution ring, or anything highly criminal, rape the local girls or whatnot and you should be fine. You won't be able to find a high paying job, but you'd have no problems finding menial labor ones. Police will even tend to treat you with more respect than the locals. Go for rural areas, where odd jobs are easier to find and the locals are willing to put up with that odd foreigner that works for food.
Uncertainty, someone could kill you on the street and no one would know who you are!
Where to sleep, where to get the next meal how to find a job, being afraid of police who are supposed to protect you, may I get some thoughts on this please?
Illegal immigrant exist because there is a community that absorbs them. This is true for all countries, asia, US, whatever. Yes, where to sleep and where to get your next meal is a problem, but not insurmountable. People with no communities to absorb them and have absolutely no place to sleep/eat? They don't become illegal immigrants in the first place. Seriosuly, why are you going to a country where you don't have a place to stay or food to eat?