Just about any bag should work if the RPi is not powered in transit. I personally keep 2 RPi, 2 Keyboard, 2 Joysticks, 2 Mouse, 2 10 inch monitors, 2 12V 15Ah batteries, 2 8A 12 to 5V adaptors, a bunch of MicroSD cards, and MicroUSB power cables in one section of my grab and go backpack that has appropriate dividers and reinforcement to keep it all safe. I do use small plastic boxes for much of it just to keep it better orginized.
I also keep an 8A 12V flexible solar pannel and charge controller in that backpack so I can recharge the batteries when outside, and potentially have near infinite travel time with the RPi's.
I would recommend adding to your list a 20 foot CAT5E ethernet cable, as many game gatherings are wired only ethernet, no WiFi. And they tend to run out of extra CAT5E cables in a hurry.
The Raspberry Pi is an ARM computer, that runs many Operating Systems, including Linux, RISC OS, BSD, Pi64, CP/M as well as many more.
Soon to add AROS to the list of operating systems.