I too traveled RTW with a suitcase and decent shoes and it helped me at the airport and hotels more often than not. I think it's easier when you need to appear reliable and clean, though there are a lot of places where it's totally impractical compared to a pack.
I did not use my cable lock at all and it weighed more than it was worth. I used the heck out of my ziplock bags and wish I'd brought more. Safety pins/diaper pins are awesome, and a needle & thread can be useful in a place where your mosquito net is torn or your velcro tent flap is worn off. I swiped an extra bar of tiny hotel soap from time to time, for when I got somewhere that the soap was not available or was just gross. Had a couple tiny extra bars with me always. Helped when camping to be able to leave the last bit of soap on the edge of the fence and not worry about packing a drippy bit of soap. The super-thin towel I bought came in handy periodically, but the sarong was the best thing ever. I had a cheap beach cover/sarong up that ended up as a dust cover, a head scarf, a towel, a clean sheet, a bathrobe, pillow, you name it. I used that thing to death. Another thing I used a lot was my floppy-brimmed straw hat. It kept the sun off, kept my race slightly camouflaged, hid my expensive camera when held instead of worn, allows you to avoid eye contact with street vendors and touts, worked as a fan and bug swatter and kept out the light when I wanted to sleep. You can hang a net off it if you have to as well, using your diaper pins. The earplugs were my best friend on the airplane or in a new place - without them, I would have gotten sick from lack of sleep and they were well worth packing. Another thing you need: shower shoes of some kind (Tevas would do fine as double-duty shoes). In cold climates or at altitude I think silk longjohns and a wool stocking cap are your best value for space. Worked for me.
Meds/Pharm: Tampax are not sold in some places. I brought Cipro from the US and needed it, and I brought stomach/diarrhea remedies for all the lovely GI tract problems one has in the third world, some safe-water tablets, a couple of flu meds, and packaged alcohol wipes with ointment & band-aids. That took up a lot more space than I liked, but I was glad I had them when sick or blistered or scratched and far from any pharmacy. Many places are so poor they cannot get Cipro and their cheaper antibiotics don't work on some bugs. I experienced that personally for four miserable days in east Africa. They usually have good ointments and sinus medications in bigger towns in the third world - tummy stuff is there too, but they have to be open and you have to be near for that to help. A roll of toilet paper, in a ziploc bag, with the tube removed is pretty compact.
I bought blank DVDs everywhere I traveled, and it surprised me that I could. I used them to back up all my photos on the laptop and mailed them home wrapped in plastic shopping bags, paper, cases if I could get them, whatever. Even in the Himalaya foothills, there were film stock shops in big towns and you could get blank DVDs. As a part-time photographer, this was a perfect solution. Not everyone hassles with a computer on the road, but as a photographer I chose to do so - it was such a lifeline that I'm glad I did, but it's heavy and expensive if it's lost. Another thing I used more than I thought was a cigarette-lighter car charger for my batteries. My driver happened to have one in Africa and we had zero electricity for over a week. The only way to get your camera batteries recharged might be in the car/taxi. I recommend a spare camera battery too. They are small.
