use handpaddles instead of a break down for 2 reasons.
1. it is smaller and you will have more room
2. you will learn to hold onto your paddle for next time, and or not chock it in a rock.
I like to put the bulky stuff up front. sleeping bag, tarp, clothes. you can stuff em all in garbage bags and then in a dry bag. use it to put your feet on. I would recomend only the stuff you are going to use regularly. if you deplete your bag over days you will have nothing left to push on as days go by.
I would have a water filter, small stove, a lashing pot and pan, unpin kit, throw bag and food(dry for long days) or pre-cook for the short ones. Dont try to prepair a meal on the river, you will need to do too much. dont forget first aid and matches!
Try to separate as much as possible and fasten everything down individualy, you dont want to loose it all in one bag. keep like stuff together, and heavy stuff by your seat back.
one idea I had was 6mm rope loops atached to the seat to fasten to. I will dig out my shit and take pictures.