On a serious note I am doubting highly that Anakin asks Obi-Wan to give his lightsaber to his child. I just dont see that as being part of his last thought before he falls. Seriously, by now he's almost completely taken over by the dark side. I'm thinking Obi-Wan picks it up and saves it thinking Anakin is dead.
he probably starts to talk $hit, like says.
"You can't win, Obi wan... if you strike me down, I shall become more powerf----uuuuuhhaahhhaaaaaahhhhhhhhhhhhh!" -SPLASH ssshsssshhhsshhhhhssssssssssssssssss!
help help! I've fallen into this lava pit! I'm not dead, but I'm very badly burned... if you could just come down and pull the release valve, I am certain I could swim to safety, thank you... uh oh, oh.. Palpatine... thank you, my lord! Thank you thank you a thousand times thank you!
Nice Black Cloak by the way, is that silk?? AUGH AUGH AUGH! The cold air on my scalded and scorched limbs is EXCRUCIATINGLY painful! Do you have any balm or curative ointments in that cloak, Master Palpatine? What's that? Sideous you say? Emperor you say... holy $hit!"
so then there is that great twist of irony in ANH, first, by Ani becoming Vader, and BEING more powerful, then again when Obi wan completes the threat, and Vader strikes HIM down, and then he becomes more powerful as the Force ghost, etc etc...
My guess is that long before the fight between Obi-Wan and Anakin, the subject of passing on his lightsaber comes up, maybe to Padme, then later Padme tells Obi-Wan. As far as his last words go, ummm, I'm guessing just a scream, or before the actual fall, probably something that has to do with vengence.