If I had three days left I would listen to music, dance, talk with friends and enjoy food as if these things were the most opulent events in my life. These things are intentionally small and common, because they don't require any preparation and still they can produce pleasant feelings.
In the mean time I would reserve 2 hours to fix my life as much as I can - I would apologize to my friends for what I have done to them and I would apologize that it took so long to apologize. This should easy my feelings. And I would write a list of places where did I store/invest my money so my family can easily retrieve them.
In the first evening I would spend a night in a bed with a paid company. It wouldn't be anything fancy since next day I would like to be actually able to do something, but it should give me a feeling that I am macho.
The second day I would do crazy things like free climbing without any protection or driving the fastest car I could get as fast I could make it. And I would visit the barber ask him/her to shave my head on skin.
The second evening would be reserved for my girlfriend.
The third day I would get a tattoo, a simple black tattoo like a pictogram of a mushroom - it takes just a few seconds to draw it but it would symbolize that I have overcame the fear from needles. And I would get a monstrous genital piercing, simply because I wouldn't have to wait until it heals. And I would abuse the strongest drugs I could find since I wouldn't have to pay the consequences. If I couldn't find anything better, I would drink as much alcohol I could and wouldn't say everyone on sigh "I love you".
When I finally pass away, it should be a few minutes before the end of the 72th hour.
And then nothing.