That's the power steering fluid container and you can buy a chrome cover and cap at a lot of different places like Race & Street. Here's the link...
PT Cruiser Power Steering Cap And Top Housing Covers Chrome : Race and Street
The air filter can be replaced by a number of different ones. The cheapest on eBay ($20-$50 incLuding shipping) and more expensive like the K&N (almost $300). Lots of members went with the AirRaid system for a little less than the K&N because it shields the warm air from the engine from getting into the filter.
Here's link to that....
PT Cruiser AirRaid Intake System Non Turbo: Race and Street
Another thing I said in the last PM is that you don't have the Vanity cover as it was made an option to buy by Chrysler and deleting it saved them some money. You have the 3 holes that hold the Vanity cover. The pins you need coast about $2 and the cover itself costs about $45.
The Vanity cover can be painted to match whatever you like and themes and pictures have been put on them too.
