I drop a pannier.

[zerodish]

As you know panniers are getting harder to get so I have trying to adapt motorcycle bags tool backpacks etc with limited success. I found a waterproof backpack near a boat dock that had been tossed out. The strap had seperated at the bottom. So I removed the other strap bottom and tied the upper straps to the rack. Today it fell off. Both upper straps seperasted. The bags do not seem to have any structural cloth but are two layers of vinyl around lots of foam rubber. But it was the thread that failed not the vinyl. I don't remember who made it but it was high end and I don't want to get sued. I took a tie down strap which I have been collectiion poked three holes in it and bolted to the bags with fender washers and one conduit clamp. I then tied the strap to the rack with an additional strap through the conduit clamp also tied to the rack. It will get two more conduit clamps at the top when I have time. I've trying to get rid of the bolts on my bags since I carrry a computer. Something to check out if you are in the market for waterproof bags.

[davidbonn]

Velcro-on panniers stay in better than ones with mounting hardware.  They are harder to take off and put on which is problematic if you have parts of your trip where you travel by train or bus, though.

The only downside is generally velcro-on panniers are smaller than other options.  Although I do just fine with two 10L velcro-on panniers, two 2.5L fork bags, a small frame bag, and a 10L rando bag.  I also have a 12L dry bag that can ride on top of the rear rack as an overflow bag.

[zerodish]

I built an emergency set of panniers out of tiedown straps that I found in the road. They are 4 inches wide and 2 inches wide which makes the bags 8 by 10 by 14. The 4 inch straps are rated at 5400 pounds each. These are linked over the rack with 1 inch straps which are rated at 500 pounds each and there are 6 of them. Sorry no photos I am between cameras at the moment. The bags are 3 pounds each. I sewed the straps together with a figure 8 sewing pattern which allows them hinge and sprayed some spray on rubber in the seams. 1 inch straps can be joined with plastic buckles which are available from abandonded shopping carts.