When the soldier boy says “I think, before I travel on, I’ll get some rest…”, he is not at all aware that he would not be able to survive after getting that ‘small pain’ in his chest. He knew that he would be all well in a few minutes or hours and then return back to his home, or may be camp. So, by the word ‘travel’ he actually did not intend any pun or word play. He only meant to go ahead. 
 
But, as a reader you should find it interesting how the poet has used the words like ‘travel on’, ‘day has just begun’, ‘getting dark’ etc. to give us a hint that he may actually succumb to his injury, that the inevitable death is coming his way bit by bit. Finally when he dies, we remember the soldier boy’s words and wonder how he may be travelling to the unknown other world that is beyond death,