Sleeping Bag liners - These are a must even if you aren't taking a sleeping bag. In hot climates you can simply sleep in your liner on top of a bed or for cooler climes you can sleep in your own liner under the covers. Either way, unless you are travelling 5 star all the way, there is something comforting about sleeping in your own liner.
Travel Sleeping bags - Choose the right comfort rating for the majority of your trip. The comfort ratings are: 7C to 20C (Hot), 5C to 15C (Warm), 0C to 10C (Temperate) -5C to 5C (Cold), -10C to 0C (Freezing). Wear clothing, combine with a sleeping bag liner and locally bought blanket to upgrade a summer weight bag
Getting a good nights' sleep is the difference between enjoying your days on the planet to hazily wandering through them. Being warm/cool and dry at night is the first step.