Mouse, Keyboard, Xbox 360/One wireless adapter, USB speakers, Logitech wireless adapter and flash drive (as you said). And that's just the stuff I have lying on my desk in front of me.
I had forgotten wireless mice and keyboards tended to have fixed cables. But Apple sells a wireless moue and keyboard. I don't see them supporting USB-A wired keyboards when they switch to USB-C. Apple TV competes with Xbox, so I don't see them caring about that either. I really don't see them supporting wired speakers of any kind (you should already be using BT ;-). I don't know what the Logitech wireless adapter is ...
For my own use on that list I am already there:
Magic Keyboard & Magic Trackpad, Apple TV, and Speakers via Apple TV. If I didn't have wireless peripherals, I'd use this as an excuse to buy them. I get gamers will not likely jump platforms to TV. But that's the breaks.
I do have a drawer full of USB thumb drives which I will have to buy about $30 worth of adapters to keep using, but this will also give me an excuse to get rid of the smaller capacity drives.
For my drives I'll have to replace a few USB 3 cables, and some micro and mini-USB cables, but again, it will also be an excuse to get rid of the older smaller drives and buy native USB-C drives. The biggest change will be Thunderbolt and Firewire 400/800 drives. I'll need new adapters for those -- hopefully just a simple and cheap Thunderbolt to Thunderbolt 3 converter.
Oh, and I will have to get an adapter for my DVD drive, though I'm suer Apple will be selling USB-C adapters going forward.