Taking a "rest day" for the hardworking White man was to maintain your tools. It was your half-day of normal work so you could leave early to do other things. Wiping off grime, sharpening, special oiling. It was a sense of satisfaction of giving some love back to the tools you would work with all year.
When I worked on the DOT survey crew, Friday afternoon was reserved for cleaning and oiling equipment, sharpening brush axes, making sure moving parts did so freely and clasps, latches and locks functioned as intended. That's also when someone got to sharpen the chainsaw chain. All that equipment didn't maintain itself, and it all spent hard time outside and needed the attention.