What to wear at 10 degrees?

Answer 1

You should wear at least a regular t-shirt, under a heavy jacket that is 100% waterproof, some fuzzy earmuffs, some mittens or finger gloves that are insulated well, some tough boots, tight sweatpants under some bigger jeans, and you will be able to stand and play outside for a while!

Answer:
In most of the world 10o is 10oC. This is essentially a cool basement temperature so a long sleeved shirt and pants will keep you comfortable for any amount of time.
In America this may mean 10oF which is about -12oC , This is decidedly cool and requires a jacket, maybe light gloves. No long underwear or winter boots are required (unless there is deep snow). Being outside for a walk in the city between buildings would only require a sports jacket.

Experimental Results:
Today was -21oC (-5oF) with a windchill of -31oC, considerably cooler than the criteria of the question. People were observed to be wearing:

• Light winter jackets (usually unzipped)
• No gloves
• No boots, just street shoes
• A few people wore tuques
  

Answer 2

At 10 degrees Celsius, it is recommended to wear a light to medium-weight jacket or sweater with layers underneath, such as a long-sleeve shirt or thermal top. Pair with trousers or jeans, and closed-toe shoes or boots to keep warm. Don't forget accessories like a scarf, gloves, and a hat to stay cozy.