"All fled, all done, so lift me on the pyre; The feast is over and the lamps expire." (Robert E. Howard)

I know this is morbid but I have always been a bit fascinated by suicide notes.
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Yes, yes, that does sound a bit wrong but it’s a strangely rewarding feeling to read someone’s last words and wonder what they were thinking at the time.
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Captain L.E.G Oates’ famous remark, for instance, as he left Scott’s tent during the ill-fated Antarctic expedition, knowing he was slowing the others down and after having begged them to leave him behind, “I’m just going outside; I may be away some time” might be stretching the definition of a suicide note but it never fails to give me chills.
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French writer Nicolas-Sebastien Chamfort’s - “And so I leave this world, where the heart must either break or turn to lead” - has always been a favourite for poignancy, while at the other end of the scale there is Hunter S Thompson (and you can insert your own ‘who went out with a bang’ joke here) whose note I find weirdly comforting:

“No more Games. No More Bombs. No More Walking. No More Fun. No More Swimming. 67. That is 17 years past 50. 17 more than I needed or wanted. Boring. I am always bitchy. No Fun for anybody. 67. You are getting greedy. Act your old age.
Relax. This won’t hurt.”

Meanwhile if you’re going to use your death to get back at someone who has treated you poorly you could do worse than cribbing from poet Sara Teasdale who left this stinging slap for the lover who’d left her:

“When I am dead, and over me bright April
Shakes out her rain drenched hair,
Though you should lean above me broken hearted,
I shall not care,
For I shall have peace.
As leafy trees are peaceful
When rain bends down the bough.
And I shall be more silent and cold hearted
Than you are now.”