Throwovers are the best bet. Clothes and sleeping bags in the panniers, stove and expensive gear in the tank bag and tent on the rack. Keeps the weight low and shouldn't fall off. Obviously take care with the exhaust, the smell of burning nylon usually only reaches the rider after their underwear has departed!.
Stuff on the forks is a pain in so many ways. It'll effect the handling for one. Not so bad solo, but two up, no thanks. It's also a pig to fasten on so it stays. Your pillion will soone get bored of a rucksack. I'd leave that plan to the Harley boys.
One idea I have seen work is under the rear rack. More bulk, but keeps it low so the pillion can get on and off.
Andy