Earbuds are useful to listen while not bothering your co-workers.
USB Type-A ethernet adapter in case I’m somewhere that doesn’t have WIFI and only a physical network port.
4-port USB hub is convenient to have and I like this one because each port can be turned on-or-off independently from the others.
USB Type-C to Type-A adapter - there are many brands around and given that the new Macbook Pro only have Type-C connections these are needed for basically… everything.
Grid-It Cocoon organizer are great for organizing your stuff and not have them flying around in your backpack. It’s also easy to see everthing at a glance and not have to search each backpack pocket.
Business cards aren’t commonly used but occasionally people do ask me for it.
There are a lot of powerbanks available but I lean towards those by Anker. The USB-C ones are great because they get charged through it and also output through it so you get an extra charging port if you have Type-C devices. The larger capacity Type-C chargers such as the Powercore+ 20100 and Powercore 13000 can also be used to charge some laptops such as the Razer Steath Blade and Macbook Air.
It’s good to keep a spare pair of glasses just in case. I have computer glasses that I keep in my backpack and an older pair of regular glasses in the car.