This assumes that you don't have access to a washing machine or launderette, so if you have access to either you can cut it by half. Logically, for a week's worth of lolita (7 days) wearing you need 2 skirts, a JSK/OP, 2-3 cutsews depending on how much you pespire. Petticoats should be packed by inverting it inside out, folding the flared sides inwards to form a rectangle, placed into a plastic bag then rolled from waistband to hem.
I also tend to buy travel insurance that covers luggage contents, because I'm paranoid and Heathrow's track record does not make me feel any better :/
Another good choice would be a long JSK/OP/skirt. A cotton long skirt would be protect your knees and feet from cold, and yet remain light enough to wear to the plane. It also has the advantage of not needing any bloomers, since the length will keep any panty flashing away.
1. DO NOT wear a petticoat. It not only gets flat, but you'll also annoy everyone else sitting next to you because you take up so much seating space. Unless you're travelling first class, your petticoat will probably spill into someone else's seat. For the same reason, I strongly suggest against wearing anything with a bustle-back skirt. Not only will the ruffles get crumples, it is also inconsiderate to other passengers. If you must, use a built-in one like those that AP and Meta has inside the skirt. Bloomers are great for this, and protect your modesty too.
2. DO NOT wear delicate fabrics like chiffon or georgette. It'll get caught on something, tear and you'll end up crying. I had the very unfortunately incident of wearing a chiffon dress to the plane (since I had a dinner event on the same night) and it got caught on the edges of the seat where chair meets the arm. Not fun, and once I landed there was a tear in my skirt :/ I repaired it later but you can still see it where the fabric tore since it's so delicate.
you *CAN* bring an empty water bottle. So bring an empty one, and get the steward/stewardess to fill it up for you once you board so you have your own supply of water. Drink enough water regularly, because you're experiencing greater water loss than on ground.
Third, bring something non-digital like a book. You could be like me with a dead ipod (died the night before), broken inflight movies and a laptop with only 3hrs of battery left in an 8hr flight. Or the best thing is simply to sleep.
be uber-careful with your drinks, especially if you're wearing Lolita. Most flights get bumpy at one point or another, and you do NOT want to spill coke all over your favourite skirt... so either wear an apron, put a napkin or such on your lap, or bring an empty bottle (though sometimes they don't even let you bring an empty bottle, for some reason...)to pour your drinks into, and drink from that instead.
Plan outfits ahead of time. This goes with any style, but Lolita especially! Are you going to a place for 5 days? Plan out 5 outfits – socks, petticoats, bloomers, head bow, everything – on your bed to make sure you have everything. You might use the same skirt twice, or put a cut-sew over a jumper skirt, but seeing how your outfits will come together will take a lot of stress off your shoulders when you’re putting your outfits on later.
Pack your good stuff, wear your cheap stuff. When you’re on the train or airplane, you have no idea if a messy child will be sitting next to you, or if the stewards will accidently spill a drink on your lap. You don’t want any of your Lolita to get dirty or ruined, but if the choice came between your $30 Bodyline dress or your $350 Angelic Pretty dress, which one would you be more upset about? Stick Angelic Pretty in your bag if you must bring it, and wear your bodyline outfit while in transit. This goes for shoes as well. Wear non-brand flats from a local store, and pack your expensive shoes. If you're going through an airplane, you will most likely have to take these off through customs, so the easier your shoes are, the less time you'll stand at customs, attempting to take off those 3-strap shoes.
I added a Baby, the Stars Shine Bright skirt (doesn't really matter the print). What I'm focusing on is not the print or color, but the fact that this is a flat skirt with no tiers or ruffles. The reasoning behind this is if you have a long airplane flight or train ride (2+ hours), sitting in one position in your seat will create bad wrinkles in your skirt, and you'll need an iron after the trip. Also, especially if you're on an airplane, a skirt with no extra ruffles or tiers decreases your chances of getting caught on something and ripping your skirt, and you are being courteous to the people who will be sitting next to you during your trip. You don’t want your skirt falling into other people’s seats.
Let's talk bloomers. You're sitting in a seat that's probably been sat in by a hundred people or more, there's a good possibility someone vomitted, spit, coughed, sneezed, stepped on, etc. on that poor seat, and you decided to forget your bloomers and put your bare bottom and thighs on this seat. First, gross. Second, make sure you take a shower directly after the trip. Bloomers are such a must for traveling, especially considering your behind is going to be sitting in mostly public places, at least in regards to getting to the place you're going. You should wear bloomers regardless, but I think traveling is one of those mandatory bloomer-wearing moments.
Bags with Shoulder Straps are Your Friend. There are plenty of sneaky shoulder bags in high end stores. You can definitely buy knock-off bags in practically any mall. They last to a point, but I've found they give me about a good solid week or two of heavy usage before threads start coming out and straps start breaking off.
Your Suitcase Can be Lolita Too! Best decision I ever made was getting a Hello Kitty suitcase. No, Hello Kitty is not by default considered Lolita style, but my suitcase matches with almost all my outfits, and when I go to pick up my bag, it's immediately recognizable.