I'm not so sure there'd be a first day in most scenarios. I think it would take a few days to really be clear what is happening in most cases.
That said though, I think the "first day" is going to be when the food riots start. When people realize that things aren't going to get better, so law goes out the window, and folks rise en-masse to loot stores. Then, it will largely depend on where I am. Hopefully, I've seen the signs, called in to work, and I'm home already. (because my work is about 50 miles from home). Avoiding the bridges, it'd be about 70 miles. Though my GHB helps me be prepared for it, it isn't something I'd look forward to us doing (my wife also works near me).
If home, I can stay relatively untouched by it for the most part at first. (and may do a little looting myself, if I can do so safely...mostly for medical drugs and fuel). We'd hunker down, try to contact friends (or hope they are on their way, or already here if they saw the same signs), and have assigned armed watches for the fences. We'd definitely confine the horses to the rear pasture where they wouldn't be seen. The big change would be losing power (at least assuming this happened before we get that prep in place). Would suck, but still doable.