Camera gear is so varied and diverse now that it's highly unlikely that two photographers will ever meet and have identical equipment in their bags. There are many pros and cons to this. On the bright side, there are many options for every piece of equipment you're looking at investing in, some cheap, some expensive, and a whole lot in between. On the downside, it can be incredibly confusing if you're new to the craft. There is a mixed-bag response too: many pieces of great gear that can improve your photography or quality of life with the camera can be missed as a result. In turn, this means you can find some hidden gems.
There are some strong suggestions in this video. For my own work, my answer to this question would be the macro slider attachment for tripods. There are many brands out there and while it's crucial for easy focus stacking, it's also great for just making small adjustments to your shot even if you're not stacking.
What piece of gear do you never leave home without?
