Other than kinks, which seems to be commonly the first thought, the Count Modula utilities are usually the ones my less-than-modular-pro brain finds the most likely to actually do what I think they’re supposed to do 
I’ve also gotten maybe slightly addicted to seeing just how many of Nysthi’s 2D I can put in a patch… just a simple, CV-controllable dual signal delay, but interacting webs of them interdicting and massaging triggers, gates, and CV?.. Daffy Duck voice MUWHAHAHA!
While folk might not consider it as being a utility module as it doesn’t sit on a signal or control path, I think of the MB browser extension as my favorite. It makes working with a huge library of modules bearable.
I work on a 15" laptop, and my eyesight has never been particularly strong. MB is, IMO, an important accessibility enhancement for rack – it makes working with rack much more pleasant.
I actually think it’s important enough that at least similar functionality should be included in rack proper,
I think at least the zoom function that we all love will baked into V2.
Rackwindows’ “Monitoring”, if we can call that a utility.
NSYTHI GraphicMeter
Handy for seeing the state and polarity of several control voltages at the same time, with the added bonus of inputs normaled to the outputs.
All the Stoermelder Pack one devices like MB, Strip, 8 Face, MIDI CAT etc make VCV Rack way more usable
nYsthi
I find myself using ML Modules’ Constants + Nysthi’s Const/Add/Mult a lot, but I also always have a nagging feeling that there is probably a better way to do what I want.
The beautiful thing is there are so many great utility modules.