At the end, Roz climbs up onto Simon's horse to ride away. She had her own horse minutes earlier when they stopped and they would have taken both horses rather than ride double.
When the group stop to water their horses at a well and they run into 4 Mexican soldiers and engage in a gun fight. After the battle, they all mount up and ride right past the well without stopping.
During the attack on the gold shipment Booker fired his cannon multiple times but he is never shown to reload it or change the aim for the second and third firings.