I have several Golden Retrievers, and I would say the most valuable command I ever taught them was "leave it." It's different from "wait" which is what I do for meal times; they wait until I put the food down and say ok. Wait means just that, wait and you can have it when I say. "Leave it" means don't touch it, and you won't ever get it either. I taught them leave it by putting a low value object on the ground (like, say, a rock, or something they just don't care that much about) then said leave it when they went to investigate. When they looked up at me, I rewarded them with praise and treats. I did this regularly, upping the value of the object, till eventually I could throw french fries at them and tell them leave it, and they would turn up their noses at the french fries and come right over to me.
When we'd go out, I'd practice leave it with items on walks, such as road kill and snakes, which has proven very valuable to me as it keeps my dogs safe! When we got the chickens, I let them investigate them, but if they got too interested they were told leave it and given a toy to go do something else with.
I have friends that used a shock collar to train leave it, which works fine if your dog needs it, but I found positive reinforcement to work just as well with my dogs.