Shopping worth it? In Europe?

I'm gonna be in Europe tomorrow and my parents tell me I should bring money to shop with but I'm not sure that the stuff will be worth it.. And I'm affraid that their clothes won't fit me... (I'm a large/XL) so I'm not sure if it's even worth bringing my money.. Let me know if you have been there before.. And what shoppes you liked.. I arrive in Paris first and then London.. Then Russia and then a cruise.