Well, you are at a slight disadvantage. The reason our ancestors relied on non-vegan foods was because they needed more energy (calories) with the least amount of effort (foraging, digesting, etc).
What I would strongly reccomend is for you to starting drinking green smoothies. Buy a whole bunch of leaves (lettuce, spinach, dandelion, kale, etc) and bananas (or other fruits you like). Put them in a blender on high speed, drink... enjoy...
Walnuts are a good filling raw vegan food. And they're pretty cheap.