Many of the airlines are getting to be sticklers and charging for luggage or even weighing the carry ons -- especially the low cost ones. It pays to pack strategically. I'm getting ready for a couple of those kind of trips. Here's some of my ideas.
Color coordinate. I can get a lot more distance from my clothes and fit better in a carry on size if I choose a color scheme. If all my clothes are interchangeable, then that spaghetti accident on day one doesn't mean I have to wear it the rest of the trip. I know none of you have this problem, it's just me.
I have a personal rule of always taking two pair of jeans or trousers or skirt or whatever due to the same risk of accident. I also take two pair of shoes. This is a personal preference because my feet will go a long way, but generally the next day they need a different pair of shoes in order to do it again. Wear one, take one in the carry on -- stick to the color scheme. As much as I want to be cool and fashionable, it may be necessary to fit it all in the bag to leave the boots or chunky shoes at home or plan to wear those each way on the plane. Only the walking worthy shoes make the cut.
I can make my clothes last and even rinse them out but toiletries for this girl are a little more tricky. That one liter bag seems to shrink as I put my essentials in it. I understand boys don't have this problem.
One tip is if you buy name brand make up and they have free giveaways (usually smaller sizes) save those for trips. Also if you go to a shop that gives you a sample of a lotion or something, keep that tiny sample dish if it has a screw on lid. That single ounce size may make all the difference from having some sunblock along on the trip or not.
I keep those little containers and clean them filling them only according to the trip's needs. The bottles and containers you buy for this purpose are often a little larger which limits how many different types of products you can take. I recently bought some shampoo type bottles. I'd be lucky to get three of them and a toothpaste travel size in my bag. I need more than three products. Look for containers that have large openings for easy refilling. The little capsule that the disposable gloves come in with hair dye is great for hair gel or creme that isn't real liquid-y.
It may sound a little rustic but those tiny bars of soap that you get at hotels can double in a pinch as shampoo as well as shower gel. If you have one of those little bars, it doesn't have to go in your precious one liter liquid bag. Leave the shower gel and shampoo at home and throw an emergency bar in the bottom of the bag in case the hotel or hostel does not provide those.
Or alternately shop on location. This is often an option but those cheap flights may be really late arrivals, or if it's an event or conference you may not be in control or in a location where you have the option to get to a shop easily.
Try to use one product for two. My face sunblock can double for the body sunblock if it's a trip that doesn't need a lot. Plus I can downsize it to one of my little containers. Conditioner will work not only to help you comb your long hair but also you can shave with it. Try to give it up a product just for the trip or plan a different hair style that leaves some product behind.
Don't forget that in addition to your travel toiletries they want you to put anything else you normally carry in your purse in the one liter bag. Lip gloss, lotion, or hand sanitizer. I use a lotion that is a hand sanitizer to combine those.
Extra tip: even when I'm checking a bag and I can put my full size bottles in. I will pack and emergency supplies type one liter, so that should the big bag not arrive, I can survive a day or two. This is usually toothpaste, toothbrush (outside the bag), make up, an eyeliner or mascara, deodorant, and conditioner.
A handy travel product if you have room is Downy Wrinkle Releaser. I just keep the bottle and mix up my own made out of 1/3 fabric softener and water, but the bottle size generally is 1/4 of your one liter bag. If you arrive, hang up your clothes and spray them usually they'll be wearable the next day without looking like they were in the suitcase.