Really love the concept of this thread, I gotta say, Anilist's discussions are far superior in terms of quality than MAL's.
Answering the question, On the first day, after quitting my job, considering I'd have the lump sum of money from selling off my lifespan, I'd order/buy some of the things that I always wanted to try, a super expensive pair of headphones, a VR headset, some other cool tech stuff, but I won't blow all of that money on the first day.
On the second day, I'd go out to my usual spots, get some breakfast, eat it at the park, have lunch, come back home, do my usual chores, spend my day like usual. But at the end of my day, I'd collect whatever personal useless stuff I got, that may have some value and put it together to sell it off.
On the third day, now with whatever money I got from selling off my lifespan + some of my belongings, I'd find a homeless person/kid, whoever I come across first, I'll then give them a get-over, open up a bank account for them and deposit every last penny I have, in it. If they're a kid, I'll enroll them in a school/college, and try to set them up with a job. Then I'll leave my home for them. And ask them to make the best they could from whatever I left and hope they don't waste away their life like me.