After trial and sentencing to being frozen, prisoners would not be allowed to keep their weapons.
As Will walks down the ladder to the alien ship and looks in the door window, you can see one of the frozen prisoners move his hand around a spear. His head is also turned when the trio walk through the door.
When the Jupiter 2 takes off, it is shown with its legs extended, yet had crashed on the planet with its legs up and sat in that configuration until take off. Also, the flying scene is the same as an earlier crashing scene but obviously reversed video, the smoke from the volcanoes can clearly be seen going down instead of up.
After Don closes the debris shield over the viewport, the Jupiter 2 is shown speeding (left to right) through plumes of smoke. This is recycled/reversed from the original S2E1 episode "Blastoff Into Space" (1967), as there is no hatch or porthole which are on the ship's "starboard side."
The strings suspending Dr. Smith's "SOS" can are visible.
Dr. Smith informs Phanzig that the prison clock has been broken for 200 years. Only Professor Robinson and West know that fact.