Besides the listings of foods that are most pesticide-contaminated (a perfect way to start), there is also another consideration: the proportion of foods that you eat. This is how experts came up with the idea of recommending that milk, tomatoes (including ketchup), potatoes, apples, etc. should be prioritized as organic for kids - because milk, tomatoes (and ketchup), potatoes, apples, etc. are what the average American kid consumes.
That is, say you buy apples (which retain pesticide rather well) maybe once a quarter at most, but you eat a few sweet potatoes every week as part of your training; that is, frequently. In that event, it could be worthwhile to evaluate whether it was better to put money toward organic apples, or toward organic sweet potatoes (or maybe better yet, just forego or eat less of the conventionally-raised apples and buy more organic sweet potatoes).
Hope that makes sense.