I'd opt for: Tri-bars and a Topeak Fuel Tank (Large) on the top tube.
You get the benefit of the extra hand positions (and, to some extent, aerodynamics) of tri-bars, plus still with somewhere to stash food to eat on the move and other stuff I genuinely would have a need for, whilst moving, between controls like a camera or battery pack to keep the GPS going.
(EDIT, done up tightly I've had little problem with the tri-bag moving around, but it's not perfect.)
I used to put too much stuff in my top tube bag and it stopped me putting as much food in as I wanted. Stuff that I wouldn't need unless I was getting off the bike or stopping properly, things like mobile phone, wallet and brevet card; they just need to go in an easily accessible pocket of the rear luggage (whether it's a saddleback, rackpack or whatever), ideally all bundled together so control stops (or shops between controls) mean taking a single thing containing them all.