It's the deathbed bit that bothers me the most- the thought that I should have made more of my life. I tried to save a life once, but failed. I let my career slip away from me.... You get the gist.
Some Buddhists do something called a 'Death Meditation' where they imagine their own deaths and funeral and what was important in our lives. It may sound morbid, but most of us live our lives like we're going to live forever. We all know intellectually that we're going to die, but we don't really understand it at a heart level. Thousands of people will die today, unexpectedly - out of the blue - and before their time; could be me even.
This meditation helps clarify what's important to us while we're still alive, so we focus on the important and not so much on the unimportant.
I think it's hugely important to consider our own deaths; I don't want to end up on my deathbed thinking "What the f___ was that all about then?"
I know this will sound a bit 'airy fairy', but in trying to find out what it is that actually dies answers a lot of questions. I mean what is the 'self' that actually dies? Yeh, I know the body dies, but are we the body? And trying to find a 'self' in amongst our mental processes is impossible too. We're not our thoughts ('I' do not choose to think what I think; thinking just happens) and neither are we our memories. Descartes tried to start from the absolute knowable (I think therefore I am) and got it wrong. He went too far when he posited an "I"; thinking is the thinker.
So what really are we? If we look closely we won't find an 'I', so if there's no 'I', what is there to live on after we die?
There's a good book called 'The Self Illusion', written by a neuroscientist called Bruce Hood, and it basically says that the self doesn't really exist (I'm not saying we don't exist - that there is nothing there - only that we don't exist in the way that most of us think we do). The question reminds me of a zen koan which goes along the lines of "What can die that was never born?"
Unless of course you believe in a soul or something; but there's no evidence of stuff like this.