If you traveling there is the reason you'll commit the mortal sin then what Pere said would apply. If you knowingly put yourself in a position you know you are very likely to commit a mortal sin you sin by going. If you just commit mortal sins by nature I suggest you work on this, say the rosary everyday and work on rectifying your internal disposition.
Now hypothetically should the above not apply, and you just happen to fall into mortal sin the things one would do is A) Say an act of contrition, and be perfect in that act of contrition. B) Go to a Priest for confession. If there is a Traditional Priest go to him. If there is none in an emergency the Church grants Jurisdiction to ANY Priest to hear your confession even if he is excommincated or laicized(It would be heresy to say that a laicized Priest is not a Priest because like Baptism you cannot take away Holy Orders). Now when I say a Priest I mean an actual Priest, this even includes the Schismatic heretics in the Eastern Rites. It does not apply to Anglicans who have no valid orders nor to Protestant preachers, Presbyterians or Lutherans no matter what they call themselves.
Should you be in an emergency and have to seek say a Russian 'Orthodox' Priest, do not participate in their masses, they are sinful to attend, just request them to hear your confession.
If noone is around and you are dying, a perfect act of contrition should suffice, make sure it is perfect.