Other than those things you mentioned, pretty much nothing. You could EV train some Pokemon and start playing competitive Wifi battles, if that appeals to you. Perhaps collect all the Mega Stones.
Or you could buy the other version if you don't already have it to see the few differences if you think it's worth it.
X/Y like most of it's predecessors, don't have much post-game content, but i'm pretty sure Pokémon Z will be the bigger, better version, and have alot more to do. You'll just have to wait a year or so for it to be released. That said, no game will ever beat G/S/C/HG/SS in terms of post-game content. :P