Here is a link to a page I found about peak mental performance under stress and fatigue. It is from "SUSTAINING SOLDIER HEALTH AND PERFORMANCE IN THE FORMER REPUBLIC OF YUGOSLAVIA" but there is plenty of good advice for card warriors.
The soldiers have a plan and are given orders to follow, but we have to be our own boss and command ourselves. I have been the most successful under adverse conditions when I had done my homework in advance- game selection, meal and break times were all mapped out. My mental energy could go into playing the cards because all the other details of the trip were worked out.
Check out the link below!