Getting into photography as a hobby need not be expensive. But charging clients for photography implies an obligation to deliver polished results. This means not skimping on the gear.
You forgot to mention a second computer if one fails then there is a second car if one does not start take extra laces for your shoes they could snap, extra undies in case you **** yourself
If this is a hobby then the redundancies aren't needed. If you do portrait sessions you should equip and behave as a professional. If you do weddings then the shots cannot be remade if something goes wrong. You really must have the redundancies or you're not really behaving as a responsible professional.
I literally have two different types of backup systems. One creates a bootable clone of my computer drive. One creates incremental backups that allow me to go back about a half year's worth of history.
I once had a drive fail completely but as I had a bootable clone, I was able to keep working while waiting for the replacement drive to arrive.
I had another drive fail slowly ... the heads were getting sloppy and "writes" we're slightly bleeding onto adjacent tracks and damaging other files on the machine and I didn't know it.... until I tried to load images I hadn't touched in a few months and found they were damaged files. I switched to the clone drive but discovered it had made backups of the already-damaged files. But since I ALSO had an incremental backup, I was able to go back in history until I found the point where no files were damaged (I had to back about a month.) Since I had that second backup I didn't lose any data at all.
Now imagine these were wedding photos, you're a bride, you find out your photographer's hard drive crashed and you aren't going to get your pictures because the "professional" photographer was not responsible enough to have a backup system. How are you going to feel about that photographer?
When I shot weddings, I had safety pins and a tiny sewing kit in my bag because we had already experienced brides or bridesmaids who had a dress tear and no to way to repair it.
If you don't think you need spare gear then I'm guessing you've never done weddings -- or perhaps just not many of them to have experienced equipment failing. Your odds of wing a lottery might be pretty remote. But the odds of having heavily used gear fail at an inconvenient time are, unfortunately, much more likely.