TL;DR - What's your most versatile mixer/ingredient?
Full story: The wife and I are headed to a "Stock the Bar" couples shower this weekend and I'm more of a "beer & wine" guy than a liquor drinker. As is the groom-to-be (we're good friends). He mentioned that part of what he's excited for with the Stock the Bar thing is getting more things to use when hosting, the ability to make cocktails when entertaining, etc. I plan to buy a bottle of Koval Whiskey (not sure what kind yet) http://www.koval-distillery.com/newsite/ as it's local and fancy enough, but I was hoping to get a couple of ingredients/etc. to go with it. Do I do a fancy bottle of simple syrup and some bitters? Or are there better suggestions out there?