Ask HN: What to spend on to maximize developer utility?

What products or services did you spend money on that improved your life as a developer with the best cost/benefit ratio? It can be anything, but I'm looking for unexpected purchases with large gains. RAM used to be the best way to save time. Then SSDs. Now, perhaps it's an extra monitor, software, standing desk, or dishwasher. Anything that offers a disproportionate improvement.