I regularly play two characters, and the way I usually do it is to ask my boyfriend to help me move the money/items. The poster above is right about a mailbox being in the works though. I'm assuming it's coming with the December update. Technically, I believe you could manipulate your two characters' retainers to help you with the transfer. If you wanted to trade X amount of gil from Character A to Character B, you could place a worthless item up in Character B's retainer for X amount of gil, set that retainer up in an empty ward, then go and buy it on Character A. Unfortunately, you'd have to deal with the taxes if you did it that way. I don't use retainers enough to know if there are any ways around that.
Edited, Dec 2nd 2010 1:01am by Kaelia88