White flour in and of itself is vegan as it comes from a plant.  The original Ritz crackers appear to be vegan since there is no animal derived ingredients in them, however, I am not sure if there is any fortified vitamin D in them offhand.  D3 or Cholecalciferol is animal derived (from fish oil or sheeps wool) whereas D2 or ergocalciferol is plant derived.  A lot of commercial foods add D3 to them which renders them nonvegan.  Most plant milks, plant based yogurts, and some other organic brands of commercial foods such as Cliff bars use D2 instead.  Commercial bread can be tricky as far as being vegan or not because there are not as obvious hidden ingredients in them such as honey, L cysteine (made from human or animal hair), and sometimes whey, milk or butterfat and other animal derived ingredients.  There are several vegan friendly commercial brand breads I am aware of such as Rudy's bread (not all of their breads are vegan but some are) and Ezekiel bread.  Some bakery breads such as french bread or bagettes are vegan friendly but check the labels.  I think the cleaner and more unprocessed the food you eat, the less you have to stress over the long list of weird ingredients and whether it is vegan or not.  Most often if I am going to eat bread I bake my own because I can control what goes into it, and really bread needs very few ingredients.  I make several loaves and freeze one for later so it lasts a while since I do it by hand.  Crackers are also very easy to make homemade and there are such a dizzying aray of vegan cracker recipes out there.  If you must eat processed food, try the organic sections because they tend to be more aware of what they put into their ingredients and tend to exclude animal derived ingredients more, although honey still seems to be put in a lot of foods.  I will never understand that since there are so many alternatives and honey bees are already in peril as it is. 

Some lists to help you decipher whether something is vegan or not are the following:

http://www.veganwolf.com/animal_ingredients.htm

http://www.vegansociety.com/lifestyle/food/hidden-ingredients.aspx

Hope this helps!