I travel with less than 10 kg hand luggage to hot & cold destinations
The 2kg remaining means that you can bring presents or souvenirs on the journey back
Wear the heaviest clothes and shoes, hat, fill pockets
Pack clothes that are made of material that does not crease
Zip off clothes that are 2 in one eg trousers, skirts
If you are staying in a hotel they normally provide toiletries and towels
If you want to take a towel suggest a mini micro fibre ones, that you find in camping shop
or
A wrap that doubles as a towel, swim cover up, evening wrap
If it is a hot country you can hand wash or machine wash using soap leaves eg
www.traveloutdoors.co.uk/highlander-active-wash/
Anything you feel you need you can usually buy at your destination (unless you are travelling way off the beaten track)
Some airlines charge you for 10 kg if you are just over the limit, so pack wisely !