I use a Brooks Flyer Special saddle with loops on my Strida. Looking around I found the classic, handmade Carradice saddle bags. I got two of them: a Camper Longflap and the small Junior. I love the look and the material.
By default leather straps are used to attach the bags to the saddle loops. This is a secure way to hold them but you have to open the flap and the leather straps to detach the bag. This is not that much of an issue because mostly you can keep them on the bike. It doesn't affect the folding.
|Modified Carradice Junior|
The bags are made from waterproof cotton duck. It got to test in with really heavy rain last month and the keep my stuff perfectly dry.