Gum
Sometimes I need to ensure the quality of my breath, so I reach for a stick of gum. However, I don't always have my gum on me. Often, I forget it at home, or at work, or in a jacket.
So I bought 5 packs of gum that I distributed to my house, my work, my backpack, and my jacket.
Charger
I like to co-work outside my house, which entails bringing my computer there. Unfortunately, my computer's battery lasts at most 2 hours. Also, my home setup is somewhat intricate, so getting my charger into my backpack is a pain in the ass.
So I bought another charger, and put it in my backpack.
Conclusion
I had an ugh field around buying duplicate items, telling myself I should have the willpower or memory to make sure I have what I need when I need it. Giving myself permission to buy duplicate items has made life a little easier, and now I'm on the lookout for more places where I can apply this. Maybe I'll have multiple copies of a book in different places.
Duplicate IDs are hard to come by. However, you might be able to have multiple different forms of ID (such as an ID card and a passport).