For Black Friday, OnePlus has a few 6T bundles and an assortment of discounts on accessories.
The phone bundles include the OnePlus 6T's regular retail contents of Fast Charger, Power Cable and USB-C to 3.5mm dongle and add a second charger and cable.
The High Power Bundle gives you a Mirror Black 6GB + 128GB OnePlus 6T and an additional Fast Charger and Power Cable (normally €34.90).

The OnePlus 6T Double Power Bundle features an 8GB + 128GB OnePlus 6T (in either Midnight or Mirror Black) and, again extra Fast Charger and Power Cable.

The last is the OnePlus 6T Power on the Road Bundle, which features the top end 8GB + 256GB Midnight Black OnePlus 6T as well as an additional Fast Charge Car Charger and Power Cable.

From there you can get a number of accessories and accessory bundles with a discount - up to 60%. For instance you can get a Fast Charger, which normally costs €19.95 for €9.97. Keep in mind that you'd need to shell out the full €14.95 for the USB-C charging cable.
For the full list of available discounts, check out OnePlus' site.