Man, I could write a book on that. My grandfather (God rest his soul, he was a very good man) supported his entire family through the depression... he was 13 in 1929, and his Mother was widowed in 1930.
He was a financially successful man later on in life, but the depression never left him. As long as I knew him, he carried very large amounts of cash at all times. I mean like $2000. It was almost like a security blanket, if you know what I mean.
He was a generous man, but never wasted money either. He paid a very good wage to his employees, and was rewarded by their length of service to him. But he was tight as a drum in other matters.
He did always tip EXACTLY 15%.
The size of the tip is directly proportional to the amount imbibed.
And I might add that in my younger days I proved that rule many a time.