The smallest quantity of powdered sugar I can get at Costco is 50#. How should I go about storing this? How do you store your bulk ingredients?

For bulk items, you may need to invest in storage bins (many come with wheels), large tubs, or large garbage-type cans. 

It's important to watch the price per pound. I've found that sometimes it's just as cheap and more convenient to purchase (25) 2# bags than one unwieldy sack of sweet cement.

Ok I wasn't sure if the dog food storage containers were adequate. I was buying the smaller bags bit Costco said they are no longer carrying them. I actually purchased the 50# bag from their bakery supply. It was $28.

Hi! Just make sure you store the sugar in an air tight container. I made the mistake of leaving my bulk bag of sugar in the bag, and it didn't last very long. It became very hard and lumpy, probably because of the moisture. Like MimiFix said, any storage bins will do.