Hi Peng,
It really depends on your type of travel.
If you are going for a walk from your home, then you can do that again...and again....so you can choose a lens to suit what you intend to shoot on any given day.
If you are travelling you need to consider some other questions:
How are you travelling?....Air, road, rail, hiking, private transport, public transport etc etc?
The answer will determine what gear to pack.
Who is going to carry your gear? Are you going to be in a heavily populated urban area or remote rural environment?
How much do you want to spend? (now we are getting down to the business end).
It all makes a very big difference.
And then ask yourself what type of photography am I going to be doing? are the shots for personal use, business, a pictorial diary, fun ..? Landscape, indoor, people, sport, macro, wildlife???? again the answers make a big difference to your lens choice.
While there are a number of superzooms on the market that will do a perfectly acceptable job in general circumstances, the primes will always provide that little bit extra, if you're looking for it.
Hope I haven't confused you....but there is no simple answer without a specific question.
Cheers.