In reply to Luci:
If you want light (but strong) and simple you need to look at Crux.
I have a 30 litre and 55 litre pack from them but you'd want something in the middle - maybe AK37?
I have a Pod Black Ice to cover this - brilliant but too heavy for your criteria. I know they make lighter versions now but personally I don't yet trust the new Chinese (?) manufacture and light materials.