First off there are 2 must have lists. Those for male player characters and those for female player characters.
For Female Player characters
Body mod: CBBE. This my own personal taste. However CBBE with Bodyslide will allow you to mimic the body types SevenBase Bombshell and UNP or UNPB. Why is this important? Because with Bodyslide all bodyslide enabled armours can be batch converted to match the custom body shape you've designed for your play through. The best mod for this is the Skyrim Enhanced - High polygons- armours (although some of the armours from this mod will have gaps - e.g the Blades armour - most will be an excellent improvement on Vanilla armours).
For CBBE I recommend you use the XPMSE skeleton and the HDT physics extension (HDTPE) and RaceMenu (3.0 or higher). Use the RaceMenu pligin from the XPMSE mod not from RaceMenu for the best customizability of your character's body. Also the RaceMenu Overlay Compilation will add tattos, beauty marks, skin effects and makeup to your character creation experience.
The skin textures I use for females are SG Renewal. Other addons worth getting are SG Female Eyebrows, Smile in HD, XCE's HD Dirt and Warpaint, Feminine Hands,
For male characters
XPMSE, HDTPE, Smile in HD, XCe's HD Dirt and Warpaint, RaceMenu (3.0 or higher) and Better Males
There are other body mods but these are the ones I use. CBBE + Bodyslide are not simply reommend due to my taste but due to their built in flexibility.