Three things
Here are 3
Pick one. Each takes about as long as it says.
Give it away while it still works
Not when you have finished with it and it is nearly dead. Now, while somebody would actually want it.
Half an hourFreeThe planet
Refill the one thing you keep rebuying
Pick a single household item and stop buying new packaging for it. One item, permanently, beats a good fortnight.
Half an hourUnder $10The planet
Mend it once before you replace it
One repair attempt, on one thing, before it goes. Most failures are a seam, a fuse or a seal.
Half an hourUnder $10The planet