At least two layers.
Think about and consider how superior double ply toilet paper is over single ply. Also, with clothing and armor. Backup generators just in case the power goes out, just like in Beirut Lebanon.
Back ups for your information, and data.
The quote, “in war, two is one and one is none.” If you’re in a battleground, or if you’re John Wick, you don’t want only one gun. You need at least two. Even when John wick goes to the party with assault rifle, he still has his pistol in his side holster, ready.
Let’s also consider the battle scenes in the Iliad, when the heroes throw spears at each other, how often the spear punctures one layer of the armor or shield, yet the additional layer saves their life.
Therefore, it seems wise that when you go hiking, camping, traveling, etc., maybe to wear at least two layers of clothing is a good idea.
Also as a parental pro tip, when you go out on adventures with your kid, putting your kid in double diapers is a good idea. Even around the house, I put on at least two layers for Seneca‘s training underwear.