A few thoughts on what you've said. First, it sounds like you're going through very rough times financially. I've been there myself and know how tough it is. It sucks, knowing your bank accounts are empty, you've just eaten the last piece of the generic bologna and now the fridge is empty too, creditors will start calling soon, payday is a week away, and even when the paycheck does come almost all of it will immediately go to keep from falling even further behind on the bills. It gets better. Hang in there.
As for Donald Trump, he (or rather his company) is close to declaring bankruptcy for the fourth time, and while he may personally have millions, he's wasting tons of it running for the nomination in a party where well over half of the members have said that they would never under any circumstances vote for him. Brilliant. He may have inherited his fortune from his father the slumlord, but his kids better be investing well now if they want to stay rich.
As for the Waltons, you're correct to say they have an almost inconceivable amount of money. But a generation ago that fortune was all Sam Walton's. Now it's split among all his kids. In another generation it'll be split again among all his grandkids. If all his kids (and their kids, and so on) have at least two children, the growth is exponential. Sure all the Walton great-great-great-grandchildren will be rich a hundred years from now, but they won't be anywhere close to Sam Walton rich unless their investments are getting unheard of returns. And you're right, they all aren't investing, at least not in a way that will bring them more money. One of the Waltons has used their fortune to build an art museum down in Arkansas that is considered among the best in the world. That's the kind of thing that can only happen when the system allows wealth to concentrate like it does. As for Walmart, I know I could (and still do) buy a lot more food there with a limited budget, and I was glad for it. The Walton's may have gotten wealthy doing it, but it helped me too.
Supply side economics is flawed, but not completely. The basics of economic math can't be ignored. You have to have people creating wealth for an economy to grow. It's impossible to tax and spend your way to prosperity. Ignore the math and you end up like Greece.