The "spirit of poverty" has nothing to do with your net worth, or your annual income.
I learned about this virtue from the SSPX, specifically the Rule, while I was a seminarian.
Basically, the spirit of poverty is about taking care of one's things, being careful with money, and always striving to minimize waste. Basically it's the original "reduce, reuse, recycle".
Do without, or if you can't do without, then fix up an old one, or buy used. If anything has value left in it, then sell it or give it away.
Leaving a plate of french fries behind at the restaurant because you're on the Atkins or South Beach diet is NOT the spirit of poverty. Those french fries will be thrown in the dumpster by the wait staff. They won't even feed the local wildlife, much less any hungry people who would enjoy them.
At the Seminary (under Bishop Williamson) even the grease scraped from the pans after the sausage was baked didn't go to waste. It was scraped into the pig slop bucket, which fed... you guessed it... the pigs! Same for the raw milk that spoiled after about 5 days. It all got poured into the pig slop bucket.
Bishop Williamson was known for writing notes on old envelopes and junk mail. No $5 package of 100 post-it-notes for him! That's benefactor money, and it doesn't grow on trees. Those benefactors had to make sacrifices to donate that money.
We also had a dedicated room in the basement called "The Free Room" where everything was free. It was like a resale shop or garage sale, only everything was free. Considering that a seminary has a lot of "turnover", that was obviously a great idea. Many seminarians lived far enough away that they had to buy airfare tickets to get home and back. So anything they wanted to "get rid of" went in the free room: cassocks, sashes, binders, clothing, you name it.
That is the spirit of poverty. It's a cross between being un-wasteful, frugal, and thankful. Plus having some spirit of mortification.