You can eat a very healthy diet, mediterranian style, even with dry and frozen ingredients. And stock up on herbs and spices. Especially herbs.

Potatoes, onions, garlic, beans, lentils, rice (brown, if you can tolerate it), frozen spinach, frozen peas, corn, collard greens, green beans, chickpeas, fava beans...these are staples for the diet. Add other cereals if you can find it, like spelt or even regular wheat, for variety. Even barley is good. Add chillies and bellpeppers (you can dry these and it will keep for months in a jar) to your pantry because you need to build bold flavours. Don't be afraid of edible mushrooms, fresh or dry.

Then add olive oil as your base cooking fat (bottled, not in a spray can) and keep vegetable based butter to top off those dishes that are a bit dry on the palate.

If eggs, milk, cheese and yogurt are an option for you, these will add some extra fat you won't be getting from your base diet.

Mediterranian diet is about eating what is available. It's peasants cooking, not palatial fare.