For chemistry, your time would be better suited to looking into which particular field suits you the most. Organic, Inorganic, Physical, Analytical, Environmental etc. There's a lot of different fields and you want to choose your field early so you can get a head start with career-wise. The same goes with economics although I'm not familiar with it so can't suggest what areas to look at.
Reading books is great, knowing what you want to do is much more useful.
For economics, try Freakonomics by Levitt & Dubner, or maybe one of those A Short Introduction books for economics, international relations, global economic history (http://ukcatalogue.oup.com/nav/p/cat...Ascend&nType=2). They will cover some of your A level course on economics and go into depth about economic theory. The books are light and not too long so you can read them on the bus or wherever!