The merits of smartphone cases are a subject of debate, but if you do use one, consider storing an emergency $20 bill between the cover and the phone.
As Reddit user Lunkavitch points out, the money could come in handy to pay a cab or lunch bill if your wallet gets stolen, or if you just forgot it at home. It may seem a little paranoid, but it's a small insurance policy that could get you out of a jam if your wallet goes missing.
LPT: Keep a $20 bill between your phone and its case. You'll have some cash if you lose your wallet | Reddit
You might already have a 
Your phone's photo album is probably filled with pictures of a fun night out, family events, and too many pictures of your pet, but the most important snapshots are often of things you wouldn't naturally think to include. As Apartment Therapy Tech points out, capturing photos of your prescription medication can be incredibly useful as a reminder or an indicator when you're in an emergency. On top of that, we'd add the following:
We've all locked ourselves out of our home at least once or twice, but locking yourself out without a way to get back in—like a phone or a roommate—can be pretty stressful. This snap-apart card fits in your wallet and turns into a full lockpicking kit in seconds. 
