I forgot how great turtle necks are on a cold day! They keep the cold off your neck. if you live in a cold region you over dress because I have had a car or bus breakdown and had to wait an hour in the cold. They sell these emergeny blankets for your car that are paper thin but hold in the heat. I recently had to wait over an hour for a flat tire and was glad to have it.
Born and raised in WI, so I can handle the cold.
On a 30 degree day, I usually wear a light winter coat (heavier than a windbreaker, but not a thick parka; I currently have a wool peacoat), jeans and a long sleeved shirt. If I like the way it looks for the outfit, maybe a sweater, but I wouldn’t wear it just to stay warm. If it’s windy, by all means, I put on gloves and/or a hat/earmuffs.
I flatly refuse to wear a winter coat if the temps are above freezing. I have a very warm hoodie which, when worn with a sweatr or sweatshirt underneath, is plenty warm.
A hat, scarf and mittens are a must.
You have to be able to cover every part of your body except the face. Your face will freeze too, if the wind chill gets nasty in which case the face needs to get covered too. Take a pair of sunglasses because the snow on a sunny day will make it almost impossible to see, and give you a headache. The sun glasses are important.
For short duration outside, I might not bother with a coat, or if I wear a coat, I won’t bundle up otherwise. If going sightseeing, I’d probably wear a sweater or an extra layer of some sort.
However, while I’ve never been to Germany, I would think that temps of “near freezing” there right now would be something of a warm spell, and that one should be prepared for something more like temps in the teens/single digits.
Please remember it’s a forecast which is why you need to be ready for worse and there predicted temperatures sound like they are the day time temps. You easily find it 0F at night and 30F at day.
Low 30s? I bundle up like a frickin’ Eskimo.
Anything under 65 isn’t fit for humans to live in. Gimme that summertime heat.
Jeans, t-shirt, quilted/lined button-up long-sleeve shirt, leather jacket. If I get hot I strip down to my t-shirt. If it’s a bit cool I leave my long-sleeve shirt on. If it’s cold I leave the jacket on.
I recommend against this. 30 degrees is not all that cold, and the inside of buildings is going to be unbearable in thermal underwear.
It is cold to someone who rarely experiences temps below 60 and expects to spend most of the day outside. And good quality long underwear (once more, NOT cotton) will wick the sweat off you even if you are overwarm, and you’ll feel perfectly comfortable.
It’s 31 today and I wore jeans, and t-shirt with a fleece over shirt to work but I’m only outside maybe 20 min all day. If I’m going to be spending time outside I’d go with coldgear Underarmor, long sleeve shirt and a quilted windproof jacket. If it’s going to be very windy or even colder I’d suggest tights under the jeans or if you get cold easily thermal underwear. For me my feet don’t really get cold so a pair of boots is plenty with regular socks for really cold days while most days I wear running shoes. But I know lots of people that wear thermal socks.
Assuming your partner doesn’t want to invest in a whole winter ensemble he won’t use again I’d say the most useful item is a scarf.
We’ve hovered around the low 30s for several days in a row here. My amount of time outdoors is minimal. To walk from the house to the car and car to work I often don’t need to even zip my coat unless it’s windy. I find a scarf helps keep in a lot of warmth.
The rest of my answer is layers. Turtleneck and a shirt or sweater over it. Often indoor temps are too warm for my outdoor preparation.
I never go out in winter without some form of turtleneck covering my chest and neck area (turtleneck sweater or turtleneck t-shirt - one or the other). I can take almost any cold weather, but not with my chest and neck exposed.
This is such a subjective question - if your friend never experiences temperatures below 60F (16ºC), he’s going to need more than a jacket and jeans. Multiple layers is probably his best bet - I usually wear a t-shirt with a turtleneck zipper sweater and light jacket - I can go from very cold to kind of warm in this outfit. He’s probably going to need gloves and a hat as well. I wouldn’t wear thermal underwear with this outfit for the reasons already given - he’ll die inside.
Yeah, if you guys think 60F is cold, 30s is gonna be Arctic weather. I nth all the layer ideas although long johns might be pushing it a bit. Hat, scarf, and gloves are probably the most important things after a nice warm coat – heat escapes from your head and neck the quickest, and fingers are nice to have. 
ATM it’s just a bit over 45F here and I’m in jeans and a thermal. Light leather jacket (more dressy than insulation) for at night when things are a bit cooler.