There doesn't have to be a specialized supplement strategy precisely for Strongman.
Fish oil, zinc and magnesium are useful in general.
Training-wise, I prefer carb shakes with some sea salt sprinkled in. When we crank up the intensity, that's all my stomach can handle, really.
When we don't do medley's or "high" reps, I can also handle protein-carb shakes, bananas, cucumbers or chocolate bars.
Bottom line is, you need some fuel for long training sessions. The rest is up to you and your physique goals.