Good morning, Suki,
This is a very interesting question! Unsurprisingly, many other people have wondered the same thing - and not just those involved in the manufacturing of these items.
In my line of work (forensic science) what remains in the ground following burial can be extremely important - though we are not usually looking for something that may have been buried thousands of years ago!
However, groups of archaeologists *have* been looking into the decomposition of different types of materials in order to try and reconstruct what life was like in the past, based upon what they dig up. Similarly, people like yourself are also wondering what will we find in future excavations - what will decompose quickly, and what may be around thousands of years from now.
I tried a slightly different set of search parameters in Google, and came up with some very interesting websites that may help you focus in on what you would like to investigate. Try searching for: "time, decomposition, archaeology". In addition to these search parameters, try including each of the different materials you wanted to research, one at a time. If some things don't work, e.g. light bulbs, try a search involving a more generic word, such as 'glass'. This should do the trick!
Here are a couple of great sites to start you off:
http://datamonster.sbs.arizona.edu/IGER ... pexerc.php
http://www.canterburytrust.co.uk/school ... scov04.htm
Please be aware that there are an awful lot of variables involved in the decomposition of different materials - so you will need to be very specific in what you choose to include in your work.
Good luck, and please keep us informed of your progress.
Best wishes,
Geoff.