where to start - well obviously the correct size for your gear !! Ive an Ozone bag thats done WA and far north QLD - fits a TT and 3 kites with harness and pump .
make sure the bag has padding in the right places. Wheels would be nice but add dead weight and I didn't go for them - but my kitebag packed up weighs around 21 kg which is a lot to lug on your back around the airport. Its pretty essential to take your fins off - even if the bag has reinforcing as either the fins will cut through the bag or get damaged. Ive also travelled with a surfboard (kiteboard) and used clothes / beach towel as extra 'bag' padding.
In a nut shell get the lightest bag that looks strong enough to contain and protect you gear!!

I think you nailed it for me, cheers Lambie