These storage protectors slot directly into the side tables in a Brinkley 3310 (and perhaps others). They keep items stored in the side tables from sliding out during travel.  The table next to the slide is especially important since items that slip out might prevent the slide from opening or closing, or even cause damage.

There are two models. The smaller plain model can be used alone, or to stack beneath the larger model.  There are two versions of the larger model, with and without a logo. 

Note that they slot in one way, tilted up on the right, then sliding down to level. (Or the left side if they're in backwards!)