For some reason, our culture declares the autumn equinox to be the start of autumn.
"Autumn" (or "fall" if you like) has no strict defining characteristics; it's a social construct, being the period between summer and winter. Of course, that's a definition in itself, but the precise boundaries are somewhat arbitrary. Why, then, would be choose the equinox as the starting point?
The equinox itself is precisely defined: It's the point at which sunset and sunrise are twelve hours apart, so day and night are equal in length. For even more precision, the astronomical definition is the point at which the Sun crosses the equator's path. But still, that's no reason to choose it as the start of autumn.
I'm greatly affected by daylight, so I consider daylength to be the most important feature for defining seasons. I take the day of maximum daylight - the summer solstice - to be the middle of summer, and the day of least daylight - the winter solstice - to be the middle of winter. Following that logic, the midpoint between the two should be the middle of autumn, not the start.
This also makes sense if we think of autumn not just as an in-between season, but as the harvest season. When we had a closer connection with food production, harvest time was culturally highly significant, and we still have the remnants of that in harvest festivals. The harvest is well under way by now, and will continue for a while yet. The equinox certainly doesn't mark the beginning of the harvest.
I realise that choosing my own definition for a social construct is perverse, but faced with a choice between reason and social conformity, I'm always going to choose reason.
One type of food that is abundant at this time of year is mushrooms. I've been gathering them for a while now, but now if I fancy mushrooms for dinner I can pop out and be almost certain of finding something. I got a good haul the other day, then yesterday I found a recently-killed rabbit by the road, so I had mushroom and rabbit stew for dinner last night. I find preparing a rabbit pretty grim (this was only the second time I'd done it), but well worth it. It's free meat, and the animal died accidentally after living wild. It's also delicious!
I have some photos of mushrooms for you, but not of the rabbit. Click through for the gallery: