Mine is this:
Sometimes, in the middle of the day — maybe I've been cleaning or gardening or something, but not exactly vigorous aerobic exercise or anything — and without any disasters having happened that produce some compelling need to do so, I'll think to myself, "You know what, I'm going to treat myself to a fresh pair of knickers".
Not a whole set of fresh clothes, not a full-on shower and change — just the knickers.
For some reason, I always mentally frame this underwear profligacy as "treating myself". It just… feels nice to put on a fresh, clean, cool pair. A little half-way-through-the-day boost.