Hi Michael,
I've been closely examining your packing set-up. What makes you different is having no pannier rack, (or panniers, of course) which itself reduces weight, although I don't know what weight would be involved in the seat-post rack itself. How much weight can you load on it?
I too have adopted the idea of dry bags secured to the front fork, for my rain jacket and fleece jacket. I secure them with velcro, one patch glued to the bag itself, then a tightly wrapped-around strip. The same for my tool pack- also very light dry-bag - secured to the diagonal of the frame in the same way. Your dry bag on the back looks very heavy duty. I have started using an Ortlieb lightweight backpack, 25L coming in at 300g. I use the roll-top clasp to secure it to the seat-post, then wrap velcro round the top of my pannier rack.
Thanks for posting the picture. It is always fascinating to see how others tackle the packing.
Here's mine.
View attachment 135080
I notice that I've moved the rain jacket bag to the back, and that's a bottle of chain lube velcroed to the frame. (Once again, I'd glued a patch on to the bottle, so that it can't slip around.). Like you, I also have the goodies bag, easily detatched from the handlebars.
Some people may think "why bother", but a couple of panniers weigh nearly 2 kg empty.
Do you use tubeless tyres? I swear by them.