We get our buckets for free from bakeries. They come in different sizes, but most are 4 or 4-1/2 gallons and all have lids. Bakeries are a great source because you know that the buckets are food grade. Best of all, they are free. There are some things that it's important to have plenty of because of the myriad of uses. Duct tape is one of these. I now believe that free bakery buckets is another. We've used several already for storing preps like grains, beans and even candles and matches. They also hold a variety of other things we always need held around the domestead.
Well shucks, if there ain't just another way cool use for these darned things. A two bucket system for container gardening. Check out this site http://www.globalbuckets.org/
I won't go into too many details because the kids on this site lay it all out very well. That's right, I said kids. Shortish people that you usually find going blind in front a video game console or texting each other across the room. These young people actually put a lot of effort into showing the rest of us how to make a very effective but simple garden bucket. This weekend we made five of them in under 2 hours. Ours are slightly different because of materials on hand, but basically the same.