Apollo 11 Spaceflight, First Manned Moon Landing

While moving within the cabin, Aldrin accidentally broke the circuit breaker that would arm the main engine for lift off from the Moon. There was concern this would prevent firing the engine, stranding them on the Moon. Fortunately a felt-tip pen was sufficient to activate the switch. Had this not worked, the Lunar Module circuitry could have been reconfigured to allow firing the ascent engine.
After about seven hours of rest, the crew was awakened by Houston to prepare for the return flight. Two and a half hours later, at 17:54 UTC, they lifted off in Eagle's ascent stage, carrying 21.5 kilograms of lunar samples with them, to rejoin CMP Michael Collins aboard Columbia in lunar orbit. During the launch Aldrin looked up in time to see the exhaust from the ascent module's engine knock over the American flag they had planted.
After more than 2½ hours on the lunar surface, they had left behind scientific instruments that included a retroreflector array used for the Lunar Laser Ranging Experiment and a Passive Seismic Experiment used to measure Moon quakes. They also left an American flag, an Apollo 1 mission patch, and a plaque (mounted on the LM Descent Stage ladder) bearing two drawings of Earth (of the Western and Eastern Hemispheres), an inscription, and signatures of the astronauts and President Richard M. Nixon. The inscription read:
Here Men From The Planet Earth First Set Foot Upon the Moon, July 1969 A.D. We Came in Peace For All Mankind.