Which tool?

For me, I have some small metric  drills in 0.01mm increments.  Although they were cheap and dull when new, they are indispensible for drilling out the snap-fit sockets of Gunpla kits.

My Optivisor is the other thing I cannot build without.  I can't build what I can't see.

A good pair of cross-lock needle-nose tweezers. I use them for everything from parts handling (plastic and photo-etch) to precise placement of decals...to picking away that one errant strand of lint or speck of dust that always wants to adhere itself to your nearly-finished model's impeccable paint finish. Also (like any cross-lock anything) works great as an emergency clamp, or one that reaches into tight corners or narrow spaces.

I emphasize the word 'good' because the cheap ones are the ones that will randomly fling your tiny parts across the room. If the needle jaws aren't perfectly aligned -- and built sturdily enough to stay that way -- they'll slip side-to-side and lose grip, hurl or bend or break those critical parts...or simply mangle your expensive PE into tiny unrecognizable spider webs of twisted metal. A few extra dollars up-front will save years of frustration. 

BTW, I'll second cbaltrin in his love for the JLC saw. A real game-changer!

Eaglecash867

My Pixnor tweezer set.  I'd be flinging parts to the carpet monster on a daily basis if it wasn't for these.

 

Sprue cutters, a fairly cheap addition but one I resisted for years as unneccessary. A huge improvement over the nail clippers, pocket knife scissors, wire cutters and (gasp) twisting parts off the sprue that was my standard for many years.

Pin vise (for tiny drill bits)

Styrene stock in sheets and shapes, brass rod, sheet, tubing used for creative gizmology (a word I have borrowed from an unknown source) to create the appearance of detail where the kit was lacking.

#1 the internet which has improved my modelling skill / ability more than any physical tool.

Optivisor: why I never considered one,I don't know.

My good set of tweezers.

Air brush: total game changer.

I could rattle off 25 items on my WB that I could not work without, but i'll just post three for now.   As an aside, a interesting challenge for everyone would be this. For your next kit, for every tool you touch, when you put it down, put it in a special place/box, and see which of your tools you have touched during the build -- would be cool find a way to monitor how many touches each one got as well, and even more interesting to see which ones did not get touched 

1) Optivisor

2) Switching from dull in under 10 seconds x-acto blades, to quality scalpel blades was a game changer.

3) This amazing Proxxon Micromot 60/E rotary tool is the most recent thing I have bought. have had it for about 12 months or so... This is the 3rd time I have posted about it in the last week 

EDIT/UPDATE Oh, I'll have to make it Four -- How could I forget this guy, the amazing JLC Saw:

My Pixnor tweezer set.  I'd be flinging parts to the carpet monster on a daily basis if it wasn't for these.