Think I read a Navy Seal once said, "you aren't prepared unless you have a backup."
1. Sources of income
It sucks to rely solely on one. You could have some reserves stored up. Emergency fund. Investments. Assets. Whatever. This is also why it's an advantage to have two people in a household earning money.
2. Extra clothes
Especially when traveling. Sometimes you might spill coffee on your shirt. Or sit on a dirty bench. Rarely need them, but nice to have.
For your house. if you live in an area where the power might go out. Know some big traders also have one in case power goes out.
Just got a small one. Love it. More room. Mainly use it to chill drinks. Been cooking a lot at home and it's been fantastic to store extra food we cook.
5. Light bulbs
Gotta have them.
6. Toilet paper
ALWAYS overstock here...
Big help if you starter goes down. Helping the 49ers a lot. Eagles won a SB a few years ago with a backup. NY Giants did it about 30 years ago too. Alabama always has a good one.
Similar to #1. Even if you don't like it, it's nice to have a skill that you can fall back on, if you need it.
Mine seems to go out when I need it the most.