There are several tournaments each year (Baltimore Teams, National Team Trials, Giant Round Robins, for example) that require more than just a few matches.
Theses endurance tournaments require extra effort because of the sheer number of matches.
You can't prepare for endurance tournaments in the same manner as other tournaments.
The main difference between endurance tournaments and other tournaments is the abundant need of stamina: not only physical stamina, but emotional and mental stamina as well.
To prepare for an abundance tournament, the key is to increase the duration of your training; that means trying to practice in increasing lengths of time while maintaining focused concentration for the entire period.
In a typical tournament you might only have to play a few matches, and so physical and mental demands are not pushed beyond your threshold.
However, when a tournament demands more matches than you are accustomed to and you surpass your threshold, the end result is physical and mental fatigue and may result in losses you wouldn't normally take.
To prepare yourself physically as well as mentally prior to one of these tournaments, go to the table tennis club early in the morning on a weekend and stay the entire day.
Play as many matches as possible and do your best to keep your concentration the entire time.
This will most likely prove to be very difficult in the beginning, but after a few weekends, you'll become accustomed to the increased workload.
This dedicated practice will really pay off when you're playing that last match of an endurance tournament with great mental and physical strength while your opponent is succumbing to fatigue.