In my work backpack, off the top of my head:
20Ah USB battery.
Laptop with charger.
A multi-tool. (Goes into checked bag when flying)
Laptop with charger.
Console cables for various routers and switches.
USB serial adapter.
Misc USB cables.
A Ziplock bag of all sorts of SFP modules.
A spare PCIe network card (SFP ports)
A microSD card with SD adapter.
A Linux live USB.
A general purpose USB with nothing in particular on it.
A spare SIM
Passport.
Seaman books from two countries
TWIC.
A plastic fork.
Cup noodles (because arriving hungry late when every eatery has closed sucks)
A pair of exrra socks.