Plastic containers with sealing lids. I haven't gotten around to getting any because I haven't had that particular problem yet, but my mother used them like crazy. Flour, sugar, anything that was dry went into a container that sealed.

I think she even used plastic pretzel barrels... of the type that you get from Sams and Costco... and sewed little decorative hats for them so they wouldn't be ugly.

Seconding the ew, though. I can think of worse things, though. :)