Call out if you're sick. Don't go in. It won't affect you at all but they may yell at you before Peak. UPS is starved for preloaders right now, they won't terminate you over calling out sick once. They basically hit the lottery with you, doing sweat shop labor for almost nothing, when most jobs will pay you more to stare at your phone.
I remember when I was in my probation period I was scared to call in sick because I wanted to keep my job. I showed up for about 2 hours, loaded the best I could, and puked 4 times. When the center manager saw me he told me to go home and call in sick the next time I was actually sick so I wouldn't get anyone else sick.
With a year in, I showed up sick, told them I'm sick, loaded the best I could, and puked 4 times. When the center manager saw me he told me to hang in there. Then, after I finished my set, my Asperger supervisor had me go clean up another belt, which I threw up on and then was allowed to go home. At least they're nicer to you when you're sick.
Edit: And another thing, if the road outside is covered in snow and you can't 100% for sure make it to work safely, call up your supervisor, say "I'm calling out, I can't make it to work safely due to the weather, you're welcome to pick me up". You hear their begging for a moment, then you hang up, turn off your phone, go back to sleep.
Twice my first year I risked my life to get to work just so they could tell me there's no work and to go home. One time I spent an hour digging the car out, was over an hour late, and I was still there before any of my supervisors/managers who insisted they needed me to come in. And there was no work due to the weather.
The point is that management is insane, ignore them.