Like others have said, processed foods do tend to all have sugar (usually in the form of high fructose corn syrup, but also as "sugar", "evaporated cane syrup", "rice syrup", etc). But plain yogurt is ridiculously easy to find. In NYC not only an you find this in any grocery store, but also most delis and even in drug stores.
For items like bread, in the grocery store, just read labels - I regularly buy bread without sugar added without a problem. In a restaurant? Its going to be sweetened. Most salad dressings are sweetened too, but just about any restaurant will offer the option of "oil & vinegar", which is just plain oil and vinegar, no added sugar.