I have friends who do 100-milers with river crossings, and, um, NO.

As far as my mileage goes, I actually checked what I needed before heading out on my last run of the month (on the 27th). And then I forgot what it was, and decided if I had fallen short by less than 2 miles I would go out and run whatever was left on Friday morning before going skiing, but fortunately that was not necessary!