Chapter 3 Mt Doom
They lighten the load, and my heart breaks with the clatter of the Sam's cooking pans into the crater. They have followed the ring longer than Gollum, longer than Pippin. And now they are gone to Mordor, never to return.
Sam's stubbornness as they climb Mt Doom is amazing, he literally outstubborns despair. It is also my best guess as to how he finds the strength to carry Frodo.
"how far is it to go?"
"I don't know" said Sam, "because I don't know where we are going."
This is the whole journey summed up quite well. They don't know where they are going, they know the end destination, but the exact how long and where is a mystery.
Frodo calls out for Sam to help him, and Sam is so tender in holding his hands. This is a true love between these two. I don't know if I buy the romantic love that some insist is there, but I will die on the hill that it is love of some kind.
We do get to see Ring!Frodo again as he commands Gollum to fuck off, and then thrice counts for all as the ring fully corrupts Frodo at the crack of Doom. Gollum fulfills his role as a walking Chekhov's gun.
The tone of the description of Frodo changes once the ring leaves him, he feels as light as he used to be at the very begining of the story.
Frodo closes the chapter by saying to Sam "I am glad you are here with me. Here at the end of all things" and it brought tears to my eyes.

Chapter 4 The Fields of Cormallen
The Eagles have Landed.
Part of me thinks of the Eagles as America in WWI and II, arriving late but not too late, especially with the Eagle symbolism of the USA.

I found this entire chapter very different in tone and composition, it felt more biblical or religious with the heaping of 'Praise them with Great Praise'
I wonder if C.S. Lewis has influence here?
The orc-clothes and other clothing being treated as religious relics also contributes to this.
I had wished for more exploration of Frodo and Sam seeing Gandalf alive, but I can see why that was worth editing out. There was just too little space.

 

... sigh. Accidentally closed my window and the draft didn't save as I typed. So overall thoughts that stick in my head from chapter 3 is the water stuff, Sam realizing they barely have enough food to make it there let alone return, and Frodo cursing Gollum with what will kill him and destroy the ring.

Chapter 4 didn't stick in my brain much somehow, it all just goes by so quickly.

Reading over your notes @Shouldabeenadog I was also struck when they didn't know how to find the cracks, and Sam holding Frodo's hands to stop him from putting on the ring. Those scenes were rough.