MJ, you know what I think it is?
While still in flight training you have money to spend but since you're not qualified yet, cannot spend it on flying. Except for the weekly scheduled lesson. So you start spending your money on stuff that you think is going to improve your flying, or makes you feel good/smart/special/important.
Once you've got the license and a bit of experience you start to realise that other than a map, a watch and a pen, there's really not a lot you need to go flying. But you also realise that the flying itself is rather darn expensive. So you quickly grow out of buying unnecessary stuff.
There's a whole market catering for the first category. This page is a good start:
Nav Kit - afeonline.com, Europe's favourite online Pilot Shop, by
And this is even better:
AviationMegastore.com
And the word gullible comes to mind: I have seen guys walking around with five different types of protractors in their pockets. How many different ways are there to measure angles and lengths?