I can live without any of them, but there are a few I've gotten used to. First to load is my personal one "Towers of Whiterun", which I haven't uploaded yet. Basically, it's a bit more content around the plains of the Hold, where there's little to keep you interested beyong the occasional deer. Just like it says on the tin, these are mostly Towers of various design, filled with Guards, bandits, Draugr, and one even inhabited by Dwemer Automata. There's also places to sleep, leveled loot, and some workstations which there's a dearth of out there.
Of the pre-made (by others) I've got Luscious Faces to pretty up my characters Kill Them Generals for when the CW arc is over so I can actually clean out the camps, Ranger Cabins II, which are handly little waystations in every Hold, and Smash Locks because none of my PCs pick them. Also, Reall Tanning, which moves Hide, Fur, and Leather to the Tanning Rack, so you don't burn them in the Forge. (Also makes crafting in Hunter's camps possible, but not Improving Armor.)
And Lastly, I have Classic Classes, and Birth Signs, which allows you to start as a Nightblade, or whatever straing out of Helgen. It's Optional, there are selections that allow you to restart Vanilla (Though you have to console in the starting spells.) I intentionally didn't subscribe to any that alter game balance, so I can continue giving advice which actually works in the Vanilla game, regardless of Platform.