My rear rack has slots on each side, near the lower part of the rack (not sure what it's for), and flashers like Planet Bike fit right on them. I put some tape over the slots' edges for a snugger fit and tied the light to the rack. Just sharing in case you have a similar rack and want to add side flashers.

Photos please.

Only good without a pannier mounted I'm assuming?

Here's a link to the rack. https://bontrager.com/model/08244
Note the small slot at the lower end of the rack near the attachment point to the bike. I'll try to take a photo later.
The panniers I have don't cover the lights, so it's quite nice!

I just use the seat-stay rings to attach them to the racks. Simple.

Above is leaving the mount on the rack itself unused , a B&M 4D top-mount rear light,
has 2 LED's on the sides, 2 in the center , with a focusing lens to increase its light .
so already visible in a 180 degree arc.
German so it doesn't blink.

Let's see if this photo works.

Nope. Will try later.

Trunk bag mount. I have two bikes and have the tail light on the bag.

+1

I used a strip of old innertube to make the mounts snug.

I think that we all need to know a little more about that life ring on your front rack.

Multimodal commuting involving whitewater rafting is my guess.

Finally got some photos:

Here's the slot where I can fit a flasher on the side of my rack:



And on the other side:


With panniers:

Given the shortening days, I'm getting ready to amp up my bike presence in the dark. I've ordered some extra lights and reflective tape (2 kinds - I'm going to experiment). This thread reminds me I have a dearth of red blinkies though that I need to address (just two, one on each bike).

For side lighting, you can also clip lights to your pannier's outer flap if you leave the zipper open just a touch. I use amber cheapie 2AAA flashers on the sides of my front panniers, which have outer pockets. These are Sunlite HL-L515, about $20 for a pair.