I use an old, and i mean real old, square plastic container my mom used when i was a kid (atleast 50 yrs old!) but all i keep in it is sugar. Still here so I guess it's not that "unsafe". As for the flour i keep on my counter i use an all-clad container that holds five pounds, but it is stainless with a glass lid.
I'm sure someone on the forums has better info than me.