These are some things that G/C 2010 Trekkers wished they left at home:
Too much stuff -- bring 1 week of clothing and leave space for souvenirs and gifts; you have to carry your luggage A LOT! The less the better.
Too many bags -- bring 1 piece of luggage and one carry-on that will double as your day bag. For more information, see the entry on luggage.
More than 1 leisure book
Converter -- heavy and useless
More than 2 pairs of shoes
Nice Jewelry -- not a lot of opportunities to wear and one more thing to protect and worry about
Hair product -- if possible, leave this stuff at home. It takes up room and is not critical.
More than one long sleeve shirts -- too hot!
Umbrella -- it won't rain enough to make this useful. It's hot and you'll dry off quickly. And, it will be in the hotel when you need it!
More than 1 pair of long pants
Money pouch -- this is also on the Good Things list (different strokes for different folks)
Hair straightener -- it's too hot and we get up too early to make this worthwhile
Hair drier -- if you can live without it, leave it at home (the hotels will NOT have a hair drier)