As already mentioned, lots of good, quality.22LR ammo, perhaps an optic, not a red dot, but good optic. Burris, Nikon, Vortex, Primary Arms or Weaver are just a few.
The most important, lots of range time. The M&P 22 is a fun rifle and a great trainer for a MSR, but it is not and was not designed to be, a “Tactical “ rifle.
Keep it simple, shoot it often and it will reward you. Once you have 300-400 rounds down range, then you will a better idea of what works, what you need and how much you really want to spend. A good optic doesn’t need to cost more than $200-300 dollars.