Here's my interpretation...
The song is written from the point of view of a mercenary soldier, (possibly Irish but I perhaps only think this because of Paul Brady) but certainly non native to the US who was on the losing side in the American Civil War.
The line 'my money here's no good' leads me to believe he has been paid in Confederate dollars, which have become worthless. The line where he can gain no credit so curses 'all foreign money' leads me to believe he's not a US national, so to him Confederate dollars and Yankee dollars are all 'foreign money'.
Not being native to the area would also explain him worrying about the alligators in the wood. He is either mistaken about the 'gators or does not know the difference between a wood and a swamp.