Since I usually use a lot of mods, RimPy (which is only partly a mod) is a must for me. Improves stability and startup time.

Other mods I can't live without:

• LWM's Deep Storage - best mod to clean up you base
• EdB Prepare Carefully - stop hitting the randomize button and just start playing the game
• Map Designer - custom starting maps, no need for seeds anymore
• Achtung!
• Area Unlocker - if you really want to organize your base you need more zones
• Cleaning Area - only clean floors that are really important
• Guards For Me - to protect your valuable pawns
• Hospitality - I just love guests in my base
• Dubs Bad Hygiene - adds more realism
• QualityBuilder
• RPG Style Inventory
• ResearchPal - Forked
• Smart Farming
• Smarter Construction - reduces building stupidity of your pawns
• Weapon Racks
• Pick Up And Haul (Continued) - smarter hauling
• [Kit] Graze up - nice for your ranches
• Giddy-up! - ride into battle!
• Stockpile Ranking (Continued) - also great for organizing
• Stop, Drop, And Roll! [BAL] - pawns don't work while on fire
• Toggle Harvest
• Interaction Bubbles - just watch your pawns having cute conversations
• Tab-sorting - great if you have a lot of furniture mods
• [KV] Path Avoid - customize paths (and avoid your own traps)
• Dubs Mint Menus - The Mint Wheel is just an amazing quick access
• Pawn Badge - make your pawn roles visible
• Snowy Trees - Before I was scared of winter, now I love it
• [WD] Realistic Darkness (Light) - because the night is dark and full of terrors

If I could only play with one mod it would have to be Numbers, but my favorite mod is Advanced Bionics Expansion.

Stack XXL. I just can't play without it.

Smart speed. Gives dev ultrafast speed without Dev mode.

I'm so used to Combat Extended at this point it feels very weird to play without it. P-Music is also a must have along with Achtung!

Prepare carefully is my favorite. Doesn't do much too change the game and makes it much easier to start a new playthrough.