By far the most likely part you'll need to replace is the rear sight blade. S&W revolvers tend to rotate sight-down when they're dropped, which will often break the blade off if you drop it on a hard surface.
The windage adjustment screw and sight blade are held in by a nut that must be turned with a special forked screwdriver. The screw is staked onto the nut with a special punch after the nut is tightened. The correct way to remove the sight blade is to tighten the adjustment screw until the screw breaks off inside the nut, ruining both. In order to do the job correctly, you'll need a sight blade, the "rebuild kit" which consists of the adjustment screw and special nut, and the "tool kit" which consists of the forked screwdriver tip and punch. Some vendors include the screw and nut with the sight blade, so make sure to read the fine print.
In terms of other spare parts, I'd suggest extra sideplate screws, a rebound spring assortment, and a rebound slide tool.