They have some potent toxins in them. Although the A. muscaria have been used as intoxicants for ages, they got listed in many books as deadly. And the US is generally a fungo-phobic. So many people are afraid to even touch these mushrooms. But they are unmistakable and it's easy to process the toxins out. So they could be a reliable harvest for many folks.

Anyway, I thought more about your question. And I think I've figured out the most unusual thing I've sampled. I was on the University of Arizona campus when the Hydrology Department's Snow and Ice Lab cleaned out their collection of Greenland ice cores. They dumped years worth of old ice cores, collected for research, out in front of their building. Some parts of those cores came from incredibly deep in the Greenland icecap, with some of the ice being over 100,000 years old. 

I raced to get some garbage bags and loaded up two big bags of ice cores -- and then got on a city bus to my house, dripping a little bit of melt all along the way. I put those ice cores in my freezer and used them for mixed drinks for months. That ice was incredibly pure and dense -- as measured in the lab, no less. It was great! And it was probably the most expensive thing I'll ever consume, too, although it didn't cost me anything. I always thought they should have made snow cones and sold them, for great science outreach, rather than just dump them on the ground to melt.