Put anything you want into it, as long as it's not flammable.
That drawer is there because sometimes manufacturers use the same frames for both gas and electric ovens, and most of the time people just expect the oven front to have a certain configuration. Since gas ovens came first, the "typical" oven design is based on gas ovens. In a gas oven, the broiler would be located underneath the oven, so that drawer is there even though it's fairly useless in an electric oven.
It's also there because what would the manufacturer do with the space otherwise? They're not likely to make the oven chamber go all the way down to the floor level, as useful as that might be around the holidays. Among other things, folks don't want to lean down that far for the bottom rack.
Since buyers don't have any strong expectations about that drawer, manufacturers of economy ovens make it as cheaply as possible, hence the flimsy construction you mention. In more deluxe versions, the drawer will be reinforced and might even have dividers or shelves.
In more unusual oven designs, such as dual-door ovens, that drawer isn't there because the space is actually useful.