Your most indispensable "tweak"?

Trying to narrow my possibilities down... 
Shunyata Denali V2 with Sigma XC power cable.  Made a believer out of me!
A pair of Bose Noise Canceling 700 headphones for my wife!

My listening room is too close to our living room and there was always the TV vs Stereo sound level battle. I lost the battle but won the war! Best $400.00 I ever spent on audio!!
After reading and thinking some more, I'm going to go out on a limb and say we're audio chefs at heart, not content to go with what the recipe dictates. 

Now, where's that herb de provence, the one without the lavender?

All the best,