We use a lot of poster board, foam paper and plastic animals around here, it seems that they are always being reused and almost always in new ways.
One way to use them is making a play land for dinos and bugs.
We chose a light brown poster board to resemble sand
I glued a piece of blue foam paper that I had cut into a pond shape, onto the poster board
I put some clear stones around half of the “water”
Added some cut pieces of wood, a stick and leaves
Added a patch of grass and a small cave house we purchased at the local pet store
Added some rocks, a small nest and plastic dinos and bugs we bought from the dollar tree
And boom hours of fun for the munchkins where the dinos have their own world.