I am trying out a what basically a waterproof bag with backpack straps on it on coming bike trip . Weighs like 250 grams and holds about 50 litres. Rolls up to about the size of a 591 mL pop bottle. Its going to see some seroius use as about 2 months of my trip I will be using it full time (girlfriend is joining me but does not cycle, bike will end up in storage ). May buid a light frame for it when this happens.