I went back through three months of my spending sheet. Total was $212 on stuff I bought specifically for this routine, and the clear winner wasn't the $38 protein tub or the $26 app subscription. It was two packs of 4-ounce glass ramekins, $11.99 each, from a restaurant supply place.
Every Sunday I portion plain Greek yogurt and frozen berries into twelve of them, lids on, stacked in the fridge door. Before that I was eyeballing a "bowl" around 8pm, going back twice more, and logging it optimistically. Now the container is the unit, and the container doesn't negotiate.
My 7-day rolling average for evening intake went from roughly 640 to 415 across about six weeks. Nothing heroic on my end, no new willpower, just fewer decisions and a smaller dish with a lid.
It's a boring answer. I think that's why it worked. What's the sub-$20 sleeper item in your setup that did more than it should have? Extra points if it didn't come from the fitness aisle.