Some simple rules
#1- Don't attend SERE in the winter.
#2- Don't spend the whole time complaining, it won't make you feel any better.
#3- Keep in mind it will all be over soon.
I attended SERE in November. It hadn't started snowing heavily yet, although we did get dusted a little. Worst part was the rain....everything was soaked, and the temp was about 35 degrees. By the last day in the field, both flight suits were completely soaked through, I stank like a wilderbeast, and my skin was numb to the cold.
Luckily, since I am ex-Army, I was used to carrying a heavy rucksack. Many of my classmates weren't so lucky, and this was their first real experience rucking in miserable field conditions.
Oh, one other thing to remember...if you're too tall to fit your entire body under your poncho-tent (as most of us are unless you're 5'2"), it's better to let your feet stay warm and dry, and get your face wet (and cold). Get those feet cold and wet, and the next day's rucking will s^ck in a big way.