Well, it's not like the show implied he blew all of his money. He even buys that tablet for himself in the very next episode.

Which, to be honest, I really like how the show handled it. They didn't play Mr. Greg off as the typical, Guy gets money and goes nuts with it ending off worse than where he began. He just went off to have a fine night with his son because he can't think of anything to do with it, while getting closer with a possible future waifu in the process.

Really, now, I can only assume the money's going to just be a way to wright around the fact he gets little business at the carwash and explain how the Gems even afford all the food, water and electricity at the house.

This was something that I was personally wondering about. Thanks, OP