You can use the snack credits for fruit, but it probably is not cost effective to do so. We were at WDW a few weeks ago (and were on the dining plan) and fruit cost about $1.25 or so, but ice cream at the parks (which counts as a snack) is about $2.50, and the large water which counts as a snack costs $2 (I think--maybe $2.50). So unless you don't think that you will use all of the snack credits it doesn't make sense to use them to buy fruit for breakfast.