It depends on the kind of set you are running, but the most common is the Power Herb + Geomancy strategy. Life Orb is a viable option too, but not as effective as the Geomancy stategy.
If this is for in-game, just something like a Pixie Plate will do.
I find Life Orb users common, but I also see Leftovers, as Yveltal is outsped by most of the Uber tier and bulky sets can be more effective. Choice Specs or Band can also be unpredictable.
Again, if this is for in-game then give it a Dread Plate or Sitrus Berry, Big Root works as we'll.