How strong polymer clay is after baking depends on the particular brand and line, how well it's baked, how thick it is in some cases or whether it has an armature underneath, and if there are joins, how well they're made.
Here are a couple of links here to a similar question about strength
) of baked polymer clays that explains a lot:
(sorry, that message seems to have been removed or something! Try this one for basic but summarized info :http://www.craftster.org/forum/index.php?topic=134056.msg1479458#msg1479458
...that post doesn't reflect that fact that the Fimos and Cernit have very recently changed their formulas so bars of the new versions aren't quite as strong as they were before, and that there is a new brand called Studio by Sculpey which is fairly
strong but different in texture.)
As for buttons, clayers have used small clay bits on crocs and on other shoes, as well as for making lots of buttons (functional and/or decorative).
Here's something from my site about it, but I don't have much more info about Crocs in particular:findings for making "charms" for Crocs (shoes with holes) are at Oriental Trading online, at least (they call them "clog embellishment doodads)
This page is all about making polymer buttons
though, if you want to check it out:http://www.glassattic.com/polymer/buttons.htm