General Tips from a travelling man
I guess my tips are good, but it depends on what type of travelling you're talking about.
killuminati said:
Yes, a towel is good for that but a towel, is also about the most massively useful thing an interstellar hitchhiker can have.
~Shard~ said:
Good one - I sometimes bring two. They are great for packing breakable/fragile items in as well, whether it be your shaver, sunglasses, etc.
TOWELS: Yes, bring a towel, but make it a beach towel. They dry VERY quickly compared to cotton ones, and they fold much much smaller. Actually, bring a quick-dry towel. They're not as comfortable though, but they fold around 4x smaller than a regular towel, and around 2x smaller than a beach towel. They dry the quickest, but beach towels are quite ace and comfy.
Bring a pillow case: If you go somewhere where you don't have a pillow, stuff your pillowcase with dirty clothes and make your own pillow!
If you go to a place where they might give you a dirty pillow case, you may get an eye infection if you ever sleep face down. That eye infection is VERY difficult to get rid of, and sometimes you might actually need a minor surgery if you don't get it treated.
CLOTHES:
SHIRTS: Bring synthetic running shirts instead of cotton ones, whether you're going somewhere hot or cold. Long and short sleeve running shirts under a fleece is more breathable than anything else, and are easy to clean, too. They pack 2x smaller than their cotton equivalents, so you could technically bring twice the number of shirts and take up the same amount of space as half the number of cotton t-shirts (ie: 6 running shirts take up the same amount of space as 3 cotton shirts).
Never bring fleece unless you're going skiing/snowboarding/climbing. They can't be packed small, although they're very breathable for sports (eg: skiing) and dry quickly.
Also bring a 2-ply Gore-Tex (XCR) jacket (not North Face, please

) because they pack very small and are extreeemly versatile.
Some shirts made from synthetic material also look somewhat dressy (IMO).

If you need to bring dressy shirts, roll your shirts and place inside an airtight bag that has had all the air drained from the inside. They sell bags that make it easy to do this. JSW already explained it, but your dressy shirts won't wrinkle this way.
Layering is better than bringing several thick shirts.
PANTS: Also bring pants made from a synthetic material. That means both shorts and long pants. The trousers look decent (ie: semi-casual) even if made from a synthetic material. Don't bring jeans because they dry slowly (in case it rains and you get wet), are dense and heavy, and feel dirty easily. You can't wash them in a sink if you have to, either.
If it's warm, bring swimming shorts or board shorts and "go commando." Why use a pair of underpants unnecessarily, or wear them at all?
SOCKS: Merino wool socks keep you warm, don't smell much even after several days of use, and are anti-microbial. They also don't lose their thermal properties when they're wet.
MONEY: Bring a money belt. Its like a very slim "waist pouch" where you can keep your money, credit cards, and passport. Keep the money belt tucked under your shirt, or even inside your pants' waistline, and nobody will even know the pouch is there. Keep all those important cards, ID, and the majority of money away from your wallet. You may get robbed and you'll have nothing at all.

But keep some money in your wallet so that you don't have to dig through a money belt in public.
PACKING A BACKPACK: There are only a few situations where you'll need to bring a backpack larger than 60-70 litres, especially when you bring the stuff I suggested.

Some people have 75-90L backpacks and I just don't get it.
Rather than packing all your most "useful" things on the top layer of your backpack, pack all mid-weight stuff at the bottom, heavy stuff in the middle of your backpack, and the lighest stuff at the top. Do this if you're THAT concerned about weight and carrying your stuff.
OTHER THINGS:
- Swiss Army knife. The beer bottle opener and can opener are actually useful.
- Pack a copy of your passport and drivers license in your bag, in your wallet, and give a copy to your parents/friends to hold onto.
-When you buy a drink, always buy from a grocery store. It's always the cheapest place. And pack fruit. They provide lots of energy and things like apples don't go rotten quickly.
- If a local starts a conversation with you, don't give them your full name, where you're staying, AND the country you're from. The combination of these 3 pieces of information is what some thieves/hustlers con and rob tourists.
I'll think of some more later.