Stronghold: Crusader: Infinite archers in a tower
If your tower is full, you can just walk the archers to the other side of the tower, and when they're passing through it hit stop to make them stay in the tower.
Stronghold: Crusader: Secret Pause Actions
Open up the Market Trade or Barracks/Mercenary Post, then press "P" to pause the game. You can purchase units or buy/sell items while the game is paused.
