So here are four personal favourites..
A light, but warm, wide-width scarf. What I love most about scarves is that it can instantly give a really simple look some edge. Great for travelling as it's light and it is compact as it doesn't take that much space. And a benefit for those who are indecisive and moody (me) when travelling, as you can add/remove this item to your look whenever you want. The simple but chic scarf can also be used as a pillow/comfort on planes when not provided. we all know how uncomfortable economy class, especially when flying alone. So get your scarf on, it will be your best travelling buddy. 
A travel-cup. You can chose whether to get a travel mug (plus side, some places give you discount on coffee if you have your own mug) or a cup and straw, I find having one close to me always keeps me hydrated. You can fill it with up water whenever you need to and replace it with purchased soft drinks to your convince. I recently purchased one for only $3 from K-Mart, Sydney.
A cap or beanie. This is personal preference, but flying and sleeping on a plane is certainly bound to mess up your hair, and what do you do on a bad hair day? You were a hat! I personally love HUF panels caps and plain beanies. I usually carry around my USA team beanie and marijuana-floral huf cap. Another pro apart from saving a bad hair day is that just like the scarf it takes little space yet makes a big impact on your style.
Sandal-like shoes. Platform shoes are my recent obsession and I recently purchased a black, sturdy-summer pair for $59 from Novo. Wearing boots on a long flight is one of my worst decisions as it's really uncomfortable to get them off/on when the bathroom is necessary and your feet don't smell exactly floral-like. Fashionable, open shoes are perfect, but make sure you carry some spare socks just in case you want to snuggle up in your seat whilst flying. OTHER FAVOURITES
Plain (thin) baggy sweater or light cardigan. Tight fitting white tank top. Long black stretch skirt. Baggy shirt and shorts. Easy to slip off pumps.
