We can't have them crossing the mountains and hiding in a cave to get out of the rain. We need this humongous fight between towering rock giants.
That was one that I couldn't remember if it was in the book or not, but it is referenced at the beginning of chapter 4.
The Hobbit said:When he peeped out in the lightning-flashes, he saw that across the valley the stone giants were out, and were hurling rocks at one another for a game, and catching them, and tossing themdown into the darkness where they smashed among the trees down below, or splintered into little bits with a bang...
..."This won't do at all!" said Thorin. "If we don't get blown off, or drowned, or struck by lightning, we shall be picked up by some giant and kicked sky-high for a football."
There are some changes to the book, but a lot of the filler material that you are complaining about was added by Tolkien in the LOTR appendices.