I have tried cattails, they're good but very bland.  They are best in the spring and early summer but edible all year long.  You pull or dig out the base of the cattail which you will find is like the inner part of a stalk of celery.  Peel off the outer parts and cut off most of the top, leaving a white pithy portion which you can eat raw.  I have heard you can also eat the new seed heads/tops of cattail but haven't tried that.  
Wild rice is ready to harvest in late August, early and mid-September.  You would have to stir it in a dry fry pan over the fire to dry it and then rub off the seed husks and winnow it or rub it over a piece of toweling to clean it and get all the husks out.  You do not want to eat any husks or get them in your eyes.  They are like velcro and will stick in your throat or your eyes and drive you crazy.  You will end up with about a half to two thirds product from what you started with raw.  Then cook it like regular rice.
Other things to eat: Fiddleheads of fern in early spring, before they unfold.  Don't eat too often, you can get chlorophyl poisoning.  Thimble berries in late August.  
NEVER eat Blue Flag or anything you might confuse it with, it is deadly poisonous.
IC