There is really no end to purifying our negative karma unless we have reached Enlightenment... so yes I agree with Helena.
However if you are always in a rush and on the go...you can still do serkym offering... just get a drink, order from perhaps the restaurant/cafe you are in and do a short serkym offering prayer. Even if you are flying you can do this although may the stewardess will look at you funny for not drinking your beer hehe...
Incense is a wonderful offering and would also purify/cleanse an area from negative energies and incense is also quite easy to bring when you travel or easily obtained... the only part that's a bit of a hassle is finding an incense burner or carrying one...but not impossible, just be creative!
So if you are wondering which one is best, there really isn't one, both are required and good, perhaps which is convenient for you at that time. And if something really bad happened to you, but you are not hurt i.e. got in to an accident, just think of it as purification
and rejoice it is all coming out now, better then later.