How to trade items between your own characters?

Im about to roll a new character but I want to transfer a couple of items to him (Like the stuff for the summer event for example).

Is there a way to do this?

Mail I assume. As long as its on the same server.

You have to Friendlist people to trade, can't friend yourself.
Now assuming everyone in your FC is cool you can have someone add your alt to the FC drop something in the box and pick it up on another character. The friendlist to send anything is part of the Anti-RMT countermeasures they have implemented, it's a bit annoying but it does hamper the pesky RMT a bit.

You can't trade anything between yourself if it's Untradable, so you're stuck in a hard place unless you have a spare account to use.