Piling on... I've written before how much I like Gamma seals for plastic buckets. If you subject them to very frequent use and keep them outdoors, the o-ring MAY eventually stretch enough to make it drop off the spin-on lid <shrug> no big deal. Perhaps that would be alleviated by lubricating the o-ring with a bit of silicone grease, but why bother?

AFIK, in the US the 3, 5, and 6 gallon buckets all use the same size lid (maybe some 3 gallon don't). Also, for the majority of the uses being discussed here, Willie brings up an often overlooked point: Use food-grade buckets. There's no reason not to, and they are more versitile containers that way - who wants to drink out of a used driveway sealer bucket? BUT...

...even food grade will eventually "pass thru" some organic vapors (petro fuels, for example), so pay a little attention to what else is stored in the vicinity. If you really want to be sure, line with a mylar bag and seal that up with a household iron.

Franchise sandwich shops also obtain many supplies in these buckets - and they may be a bit aromatic at first. A good scrub with dishwashing detergent and a few rinses later, fill with cool water and add plain old bleach - as much as 1/8 cup or so per gallon (it should be pungent with chlorine smell) and let it sit in a safe place out of the sunlight for a few days. Dump into the sanitary sewer and rinse - should be good to go. Pickle buckets seem to be the toughest to deoderize but I've found that a week or so in the sunlight after sanitizing usually does the trick.

Buckets + gamma seals are awfully versitile.