Preparing for a party, I just bought $20 worth of food at the grocery store. I added it up and the food had ~6000 calories. I bought enough food to fully feed a grown man for three days, and it only cost 2 labor-hours worth of money. The modern world is amazing.

Edit: Guys, I realize this is neither a healthy diet nor the absolute maximum calorie/dollar that you can get. I also know that the US minimum wage isn't enough to live on and that there are other costs of living besides food. This is /r/showerthoughts, it's a thought I had, let's move past the nitpicking.