I think the answer to why he spent $20 is desperation. I don't see this as anything new you see it in the casino's all the time.
Stupid as it is, I guess it works every one in a billion times.

I remember I had a friend that was down to zero dollars in her pocket out of the kindness of my heart I gave her $10 as it was all I had in my at the time.
She went out, bought a magazine, a sandwich a cup of coffee and cigarettes. If I was that deeply in the hole, I could have made that $10 last a week buying food like veggies, bread, potatoes etc.

If nothing else it taught me a lesson.