I thought i was in one before at the enchanted kingdom ( start city ) I was going to buy this bag that let me carry 100 more coins, but now I can't find that thing anywere.. help please!!

Yeah, the store is under the stairway that leads to the throne room. You'll see a little open stand setup right underneath, which is right across from the waterfall.

You can buy more bags at other stores as well, the maximum is one that carries 999 runes.