What foods have high sugar that you wouldn't expect to?

That depends on how well informed the person is about food. There are many misconceptions about foods which are too high in sugars, like carrots, or fruit. The main surprise would probably be potatoes. They're actually complex carbs, but they breakdown so quickly they act like simple sugars. As with anything, that doesn't make it a no-go food, it just means you are mindful of the quantity. Same thing with fruit. A few portions aren't going to hurt a diet, but eat dozens of portions or drink litres of fruit juice and you'll be overdoing it.