The friend who travels with you

I am trying find a phrase or just a word that expresses the friend who travels with you along your trip or journey.

You are my best ____ .

How can I call this person?

Solution 1:

Companion means exactly this, without any addition. The word has expanded over time, but the original sense (and meaning 1a in the OED) is

One who associates with or accompanies another; a mate; a fellow.

You could use any of the following:

travelling companion / travelmate / travel partner

Myself, I would probably favour "travelling companion".

Edit: As several people have pointed out, the word "companion" alone would be sufficient.