I put the chain in the bigger tail bag, coiled up like a snake.
That leaves plenty of room for my jacket liner, bottled water, etc.
The locks go in the smaller tail bag.
The chain is a Kryptonite Fahgettaboudit, 5' long, and has a powersports warranty. If someone compromises it and takes your bike, you send them a link or broken lock, and they will pay up to $1250 of your insurance deductable. The first year warranty was free and just a few bucks for up to three years. It's heavy, at 15lbs, but it's worth it.
The disc lock is a Xena. I think I got both of them from eBay.
I work in downtown Kansas City and have to park in a surface lot right next to a bus stop. I lock it to a bicycle rack through the rear wheel and put the disc lock on the front wheel disc. So far, so good.
WGW