As someone who probably falls partly under your definition of 'wasteful':
I don't like planning, and I forget things. So I sometimes leave the light on when I leave the house, forget something when I have to do groceries at the store so I have to go back, if I have half a meal left, I throw it out rather than freezing it, etcetera.
I've learned that, for me, accepting that gives me more peace of mind than trying to plan every part of my life. It also wastes less time than being super organised with my groceries, and I also end up throwing out less if I just shop for a single meal at the time.
Still, my spending is not that high, and my ecological footprint is not big. I switch electricity companies each year, taking advantage of their sign-up bonus. I make sure to double check that I've turned of the heating when I leave the house. I only have LED-lights in my house. I invested in solar panels, which will take a long time to earn back. I bought a house that is 20% cheaper than what I could afford. When buying the house, important factors were that it was well isolated, and that my commute is short, cheap and fast (20 minutes by bus). I compromised on its garden and square footage. I buy a phone that's 300 euro rather than 700 euro and use it until it breaks.
To me, 'don't be wasteful' is best applied selectively, both ecologically and economically. I approach it like an optimization problem: Identify the bottlenecks and attack those.