Courier Post deliver all of mine, so they're obviously happy to take them.
Dont feed the day before shipping, fill the Bag with enough water to cover the Fish, then fill the Bag with Air.
Double or Triple Bag as Hans said.
Pack securely into a Poly Box with Newspaper and Heat Pads.
I usually do a Water Change the morning of the night they are going to be Couriered.
Good Luck :-)