The interlocking containers lock in and are very secure. They are handy when using powder mixes during the day. Just put your powder in the storage container, stop and pick up a cold bottle of water, shake it up, and enjoy. I bought it for me, but my husband has taken it over. He puts his vitamins in one continer, powdered collagen in the other, then mid-morning he grabs a coldbotte of water, mixes his collagen, takes his vitamins, then enjoys his drink. It is good for Crystal Light individual packets. Empty the packet in the small container; or use 2 different flavors of Crystal Light, one in each container. Then, when you want a cold drink, add cold water and ice to the large bottle and add your favorite powdered drink mix. You can mix it fresh. You dont have to carry around the same drink you mixed up before leaving for work. It gets warm throughout the day. The bottle isnt really large. It is just the right size!