The Vittles Vault line of stackable containers are very popular for bulk grain storage.
They are food grade and airtight. They have a large easy access opening and the ability to stack makes them space efficient. Heavy Duty construction and easy spin off and on lid. Lid features lock-down double gaskets. The body includes molded handles for easy carrying. Made from FDA approved Food Grade Plastic and BPA Free.
This one is rated for 50 lbs. The 50 lb rating means it should hold a sack of grain.
10/20/17 1 AM Central: This highly rated container has dropped to $19.59. That’s the best historical direct from Amazon price I found. Shipping to most US addresses is also free with Prime Membership [Try Prime for Free] or a qualifying order. Price, shipping and availability can change quickly. Check the product page for current price, description and availability. Also: Recent Amazon Finds and Amazon Fillers Resource Page
Vittles Vault 50-Pound Stackable – multiple size options available