I remember when my old cat died very well, her kidneys gave way eventually. It was 5 years ago now, one thing which will stick in my mind was the "miaow" she did one morning. My wife said, is she hungry? and I answered, "no...she will go tonight, I can tell from that miaow"
It was something in her "voice", I just knew that day was going to be her last. That evening she had some food and then sat with me for a bit. Her eyes kept going to a distant stare and her head would droop, then she would snap her head back up and her eyes would light up again. It was like someone turning a switch on and off over and over in her head.
The wife and I went to bed as normal that night, I carried our cat up to bed with us and she lay next to me. After a few hours she gave a miaow, then laid down and just went. That was it. I think it was quite a nice way to go, together in bed.
We buried her the next morning in a pet coffin in our garden, along with her favourite toy, blanket, bowl and a photo of us