Um...the food is very much the best idea.
It's really, really the best idea.
I cannot imagine how much their rations must suck.
Yeah, especially when you remember that the forces are the Western Approach which is a desert. If normal military rations are bad, those guys have probably be given stuff that'd have been made with those arid conditions in mind, where normal food is going to not remain fresh for very long.
Cullen's suggestion to supply them with some fresh food, even if it's a hassle shipping it out in the middle of nowhere and needs to be done regularly because it'll spoil quickly, honestly is the better morale booster as it shows that the Inqusition cares about them and acknowledges that they've got the absolutely worst post out of all three Keeps in the game.
Sure, Emprise du Lion has Red Lyrium growing everywhere, but at least their Keep there don't have to worry about refridgeration for their grub. Plus they have rebuilding the town to keep them busy and get to relax by having the odd snowfight or making snowmen on their off-hours... the guys in the Western Approach are stuck between the Abyssal Rift and sulphur pits, with nothing to do!