What's your favorite "frugal win" that saves both money and time?

I've been trying to be more intentional about saving money, but I also value my free time. Lately, my best hack has been a simple "meal prep Sunday" where I cook a huge batch of rice, roast a big tray of vegetables, and grill a bunch of chicken. It costs a fraction of what ready-made meals or daily takeout would, and it saves me from the "what's for dinner?" stress every single weeknight. I probably save a good 2-3 hours of cooking time during the week and at least $50-$70 on last-minute food decisions. It feels like I'm buying back my own time.

What's a frugal habit you have that actually makes your life easier and less stressful, not just cheaper? I'm looking for more ideas that are efficient in terms of both money and time.