I grew up in a poor family. Not poor enough that we ever went hungry, but that was partly because of the generosity of friends/family who would sometimes buy us groceries. Us kids certainly never got new clothes (there was a steady stream of hand-me-downs from the older kids and other families we knew).

Being self-employed, my dad's income was irregular and often came in $5000 chunks. You might call that a windfall, but my parents were disciplined enough with their money that it automatically went into a savings account for the next mortgage payments, or to pay off credit card debt[1]. We weren't suddenly going out to eat when a cheque came in (in fact, when I was 10 or so, I remember helping my mom enter receipts into her big accounting book, and the total restaurant expenses for the entire year was something like $30).

I don't think we were ever officially under the poverty line, but with a family of 11 in a high cost of living area, the money had to go a lot farther than normal.

[1]: Unfortunately, they weren't disciplined enough to build up and maintain an emergency fund to carry them through rough times, so they relied on a low-interest credit card for essentials way too often.