Ear plugs and neck pillow...
Several sets of ear plugs are a huge must to guard against roommates that snore, noisy neighbors, traffic and screaming babies on a plane. I keep mine permanently in my backpack and carry them on board planes, trains and automobiles. Ditto for a "blow-up neck pillow." Always keep it handy. I find mine both in travel shops and shops that sell bath equipment.

Grapefruit seed extract...
A tiny bottle of grapefruit seed extract will last forever. I use it to keep parasites at bay when traveling where intestinal "critters" are a concern. A dropper in a cup of water is super bitter, but can be helpful in protecting your tummy. Ed. note: When it comes to things you ingest, I always advise that you check with your health food store or pharmacist to find out more about the product and whether it will work for you.

Yogurt...
Local yogurt can help avert traveller's diarrhea by initiating healthy bacteria into your system. It'll work to gobble up the bad guys in your tummy. Just be sure the yogurt is packaged, pasteurized and safe. Eat a cup every day and, to start you off right, don't forget to begin eating yogurt with live cultures before every trip.

Emergent-C...
These little packets mixed with water, taste like a lemon fizzy, are full of vitamin c, magnesium and more. They're inexpensive, found at health food stores and take up little room in your bag. I'm told they're the best for boosting your immune system which can suffer during travel. Plus, they work wonders for me on a Parisian red wine hangover. I also take one on the plane to counteract all the airplane germs.

Blueberries...
Dried blueberries are great for stomach upset too. The grocery chainstore Wholefoods stocks them. Most likely, your neighborhood co-op will too. Ummm, yummy antioxidants.

Ginger candy...
If you have trouble with motion sickness, eat a piece of crystallized ginger. It really helps me to ease the nausea. I buy these great ginger chewies that are wonderful at the Chinese grocery store. They're sort of spicy - I share them on the road - a great way to meet people.

Tiger balm...
This is my secret weapon for pain. A tiny tin lasts a long while and a little rubbed on a sore muscle or on my temples warms up the spot and rids me of head or muscle aches in no time. Get the colorless one in the red tin at most drugstores.

Extra eye glasses...
Bring extra glasses should you lose or break your pair. Take along good sunglasses as well. Wear these to look exotic and to keep your eyes safe while you're exploring new territories. Best of all - use dark glasses to shield your gaze in macho societies (where even a short eye lock with a man can lead to unwanted attention).

A sarong...
A sarong doubles as a table cloth, a picnic blanket, a curtain in a room or train car without one, a cover for your hair and shoulders should you need a cover up, a way to change in/out of your swimsuit, a blanket, a bandage, to cover your knees for modesty in a cathedral. It hardly takes any room in your pack and, you can even wear it as a skirt!

Toilet kit...
I carry a toilet kit that has a hook and a mirror. Usually there's somewhere to hang your things, but there's not always somewhere to set supplies down. Plus, you never know when you need a mirror on the road.

"Shout" stain wipes...
These are a staple in my backpack.