Firstly, prioritise. What do you think is most urgent? Write these tasks down in order of how important they are, start at the top and work your way down. I would say that learning AS physics, researching unis and starting your PS are the most important, seeing as you want to apply to Cambridge and the deadline is earlier.
Then, take each task and break it up into more friendly chunks. For example, for the "learn AS physics", make a list of topics and do a topic a day. Cross them off the list once you are happy with them, and the whole task seems more manageable. For the "research unis", draw up a list of things that you want from university - location, distance from home, course structure etc, then look at all the universities that meet your criteria. Try to visit some of them in order to narrow down your list. From your sig it looks like you have an idea of where you want to apply anyway, but don't rule anywhere out just yet as your AS results could affect these, or you may just change your mind about one of them.
Remember to enjoy your summer as well! There are a few things that look like they'd be beneficial to do, but remember you need a break otherwise you'll burn out quickly when it comes to going back to sixth form/college.