While I will do both road and mountain bike touring (bike packing) my passion is mtb backpacking. I ride a full suspension bike because I tour on the roughest most technical trails when I can. That limits the rack and pannier situation, so I had to get creative.
A few requirements for my riding are 1. need to be able to get off the back of the saddle for steep descents, or maneuvers (can not stack stuff on the rack). 2. need side frames on the rack to support panniers and 3. need tire clearance for 5 inches of wheel travel.
Bar bags are no good for maneuverability, I still ride 18 inch obstacles fully loaded.
All the bags I was looking at were either too tall, too heat, too bulky, too expensive or too cheap to work for mtb'ing. I decided to make my own panniers. Luckily I had a soft cooler a Wachovia bank employee gave me, and I was able to get a 2nd matching cooler. These were small enough, but had a lot of features including 3 exterior pockets, zipper top opening, fully waterproof interior (since it is made to be a cooler) and even handles on the top.
I searched all the post mount pannier racks and decided that the Civia Loft rack was my best option.
I added an aluminum backing inside the pannier, attached hooks and made a locking mechanism to secure the pannier. They fit perfect on my rack.
I estimate these hold about 15-20 liters of gear each - my sleeping bag almost fills one with only enough room for a few items stuffed on top of it.
I was especially happy with the mounting system. That took many months of thinking to come up with. the upper hooks were no brainers, but the attachment system on the lower mount, although stupid simple now, were an engineering manifest. It's tool free, light, easy to repair and can be done blindfolded.
I would like to see others homemade panniers and bike packing gear.