Hi Andy,
I hope this is helpful and not patronising, but then, (I think it was Bambodoggy who said this first), I don't know what you know already.
Maybe we could look at it from a different angle and ask the question what will your body really need during the trip?
Assuming that (with the exception of animal / bird / fish flesh) you will be eating more or less the same as everyone else does, and that they will all be getting a fairly balanced diet, then all you are missing is a couple of hundred grams of protein a day. This is not so big a deal if you are watching tv on the sofa all day, but if you are man-hauling heavy packs across vast distances you are going to really need to ensure your protein intake is up their with everyone elses. You'll also be consuming more food in general than you normally would.
I am assuming that you are veggie and not vegan? If so then you should try to make sure there was at least some milk / cheese / eggs in your diet at regular intervals, and preferably in good sized portions.
Vegetable protein can be obtained by mixing grains and beans or lentils or nuts. This ensures that you get all 8 essential amino acids, though you'll need to eat more than the carnivors to get enough protein. But go easy on the nuts, it's not so great to eat more than a few handfuls a day as they're 50% fat. Same goes for the cheese.
I would also consider taking some of the protein supplements that body builders use. You can buy them in big tubs of powder and in the form of chocolate bars. This could be a useful addition to your diet and many of them are veggie as they are mostly whey.
If I was doing the trip I would be looking at this kind of stuff:
Breakfast: Some kind of porridge with dried or fresh fruit and nuts, can be made with milk and you could add a boiled egg or two to the menu.
Lunch: Eggs or cheese with some kind of bread.
Dinner: Rice with beans or lentils and vegetables.
Snacks: Anything high in energy and in protein. (Meusli bars / snickers cruncher / chocolate).
Of course there are a hundred different variations on this theme but it's basically 40% grains (carbohydrate), 30% Eggs/cheese/nuts/beans/lentils (protein) and the rest fruit and vegetables. (Vitamins and minerals).
To add some more detail, most of the common veggie burgers / sosmix / TVP etc would all come under 'beans' because they're mostly made from soya.
So, if that's what's good to eat. How are you going to get it?
Well, I'm no expert but I'm guessing that like most things it's going to have to be a compromise. You'll probably have to carry a lot, be flexible about what you eat, and use every available opportunity to stock up.
Finally, if you can get hold of an army veggie 24 hour ration pack at least you 'll know what they survive on. Though there's no chance of carrying 30 of them as they weigh a fair bit