Pro-bundle method! I went to Italy for nine days last fall and in addition to the standard clothes, accessories, & toiletries...I also had to pack a 60 meter rope + personal climbing gear. The bundle method was my hero. It was ridiculous what I got into one not-quite-carry-on sized suitcase and a moderately-sized day pack.

I even had room for three bottles of wine and olive oil on the way back.

One caveat - if you're going to be moving around a lot, bundling can be a little annoying since you have to unpack the whole bundle to get to anything in the middle without messing it up.

Personally, I always take at least spare underwear in my hand luggage. I will never forget the time the airline misplaced my luggage and it had the contents of my entire wardrobe in it. It arrived three days later, but wearing the exact same clothes for three days is not great.

If you are going anywhere international or for any lengthy period of time, take a bar of Leggitt Shampoo! 24 washes; small space; no spillage; all natural....hard to beat it. (Sells on Amazon.com)

Then Neutrogena makes a face/body bar. All the same description except for the natural part.

A Hefty zip lock bag (purple tab pull across) makes a great cosmetic and/or toiletries bag: no heft and easy to find things. The Hefty is easier to lock and unlock with the purple tag than any other brand.

Take a few kitchen tall trash bags. Handy for wet or damp clothes or for keeping dirty laundry apart from the clean stuff.

For pills, buy a fisherman's tackle plastic box with all the little dividers. Make sure you have a place for each type of pill. Peel and place the labels from the bottle on the inside and outside of the cover as well as the bottom outside. Nothing big with levels or heft...just the boxy plastic container with dividers.

Layers of clothing that is interchangable for color coordination. I keep color on top and neutrals (white, black, khaki...) for skirts and slacks. Cotton pants dry faster and better than jeans if you need to do laundry on the road. A couple of sweaters that match the pants and I am good to go....and go....and go...
Hope this proves helpful to someone.

i always cable tie my bags shut if i'm checking them. i know the tsa can open the locks and likely will. the cable tie is easy enough for them to break, yet lets me know if someone was in my bag.

I second MatildaScott's suggestion to bring a spare pair of undies in your carry-on, though I would suggest going a bit further and pack most (if not all) your undies in your carry-on, in addition to 1 extra outfit. After having my luggage lost for my entire 2-week stay in rural Austria and Italy last Christmas (thank you, Frankfurt International Airport) and not having it returned to me until 3 months (!!) later back in the US, I only survived by packing a pair of jeans, spare t-shirt and hoodie in my carry-on. Sadly, I had to buy all new undies which costs more than you'd think!

My husband is in the military so we travel and move more often than I'd like. I ALWAYS roll our clothes. It's amazing how much more you can fit in your suitcase! It also helps to keep things more organized. If I have some I CANNOT roll, I simple put on top, neatly folded of course, before zipping up! Works like a charm.

I'm one of the rollers-up as well. Went to New York for 2 weeks, and only took one very small suitcase! Works like a charm!

Most of the clothes I take with me on trips are always items I planned on donating/throwing out, so I don't have to lug them all the way back, but simply throw them out/donate when I'm heading back. This way I can stuff my tiny suitcase with items purchased on vacation! And I keep one great outfit in my carry-on.
Same goes for toiletries; I only take some leftovers with me so I can throw away the (nearly) empty bottles/tubes at the end of the trip.
Oh, and I only take clothing with me that I can mix and match.

I traveled extensively for 2 years in 3rd world countries with only a backpack and I SWEAR by rolling my clothes up. Pack versatile clothing (i.e. each piece MUST be able to be worn with 2+ other pieces) and if you're going for 7 days, don't bring 7 outfits. Especially not on a beach vacation. Because, come on, that's just ridiculous.

Also, avoid traveling with annoying overpackers because they will ask you to haul their stuff even when their luggage is much larger.

I'm curious though: Why encourage people not to lock their luggage? It's a very good idea in many countries where airport staff have been known to go through luggage and steal things (my boyfriend had his cigarettes and a piece of clothing right out of his bag in Indonesia at a point in our travels when only the airport staff would've come into contact with the bag).

Will start rolling next time! I also only bring clothing that matches everything else I bring. Since airplanes are usually like refrigerators, I always bring my most heavy sweater as carry on, even in the summer.
Finally I bring a lot of gifts with me when I leave, so I can use the space later for bringing stuff home!

I do background on a lot of tv shows and they'll ask for four complete suits with optional changes. I stack them all on top of each other with the hangers still attached, then use the hangers as my base as I roll them down. Using this method I've gotten four full suits plus 2 pairs of shoes in a BACKPACK with no wrinkles. When you live on the top floor of a five story walk up, you don't want to be dragging a suitcase to set. :)

Crate and Barrel sells a wonderful 1 qt zipper top clear bag designed to pass TSA inspection. We also pack clothes we don't intend to bring back (same for nearly empty toiletries), and we like to roll our mix & match clothes. I suggest women always bring a cheap pashmina wrap -it comes in handy to keep warm & cover up! I also cannot live w/o a bandanna (for drying hands/sweat) and exofficio underwear. I can travel with just 2 pairs, washing them out in the sink each day is so easy! We also always pack t.p. and hand sanitizer. For the airplane, I wear my largest shoes (hiking boots on the last trip) and wear layers. I also wear or tie a jacket around me just in case. We were just in Tanzania (and made it to the summit of Mt. Kilimanjaro!), & I mostly wore pants and a fleece!

Bennemans, are you saying you just throw away your clothes after you travel?! That seems incredibly wasteful. How many clothes do you have?

My best tip for traveling light--what you absolutely, positively <<must>> have are medications, identification, ticket/boarding pass, and money or access to money (debit/credit card). Now, relax and do your best to pack light. Anything you forgot you can beg, borrow, or buy later.

In the US, you are not allowed to lock luggage anymore (post 9-11). However, you can buy combination locks that are TSA approved. They have a keyhole in the bottom that TSA agents supposedly have a master key to open. Here's a link to the explanation on the TSA site: http://www.tsa.gov/travelers/airtravel/assistant/locks.shtm

I use one all the time because that one extra level of security gives me piece of mind. However, while travelling this April, a TSA agent asked me to open my carry-on and I told him he could open it with his key. He looked at me like I was crazy until I explained how it was a TSA lock and how it works.

I do the "toss the clothes" thing too. When it's time to clean out my closet, I set aside things I don't want anymore and take a few with me on vacation. Then I just leave them wherever I'm vacationing.

I also don't believe in checking bags. I made it for a 1 month trip to every climate you can imagine (everything from 90 degrees in the shade to below freezing) and I fit it all in the airplane cabin with me. It's not hard.

for our 2 week Great Britain trip, I bought those "Space Bags" on a whim...thinking it'd be funny if nothing else. They...saved...us! Dirty icky clothes...into a Space Bag! uh oh...not enough room for those shoes from London? More clothes into another Space Bag! They really do save you room, and help keep clean/dirty/wet clothes from touching each other.

I use gallon-sized Ziploc bags much like the Space Bags you see on television. Depending on the trip and what I am taking, I separate clothing into like items (shirts together, pants together, etc.) or outfits. Then, I pack the bundles into the bags and press all the air out before sealing them. Besides saving space, this protects the clothing from leaking bottles or spills and keeps the suitcase very organized.

I once packed four ball gowns, four days of street clothes, stage makeup, jewelry, and two pairs of shoes into a carry on bag, and still had room for souvenirs.

I'd actually amend the lock recommendation: bring it for the hotel. I can travel for a month, including a musical instrument and grad school text books, with a carryon and a bookbag, but not if the hotel staff is going to swipe my wrinkle-free, stuff-anywhere, wear-anywhere wrap dress.

Clothes that I am about to throw out are certainly NOT the clothes I'd want to be wearing on vacation!
I also swear by rolling