2021-09-19 (updated 2021-09-19)
The player can purchase certain items in shops that immediately kill Gordon. Others will end the game. So, only buy the items you need. Trial-and-error will let the player know the difference.

The left door of the doors to the bedrooms has a game ending bug.

The oyster will instakill Gordon when it's mouth is closed. To survive, Gordon must enter the oyster's open mouth.

Invincibility
From the title screen, press and release each key in this sequence: Pause ↓ 1 1 2 1 Pause. There is no feedback to let the player know if the sequence was entered correctly.
All Items (except space suit and instadeath shop items)
You must get the salami and cat first. They are in the kitchen. Then go to the children's bedroom (Go left to the next screen and into the first door).
Hold ← & ↑ simultaneously, press and release 1 & 2 simultaneously, then release all controls.
The space suit can only be acquired by trading the pearl or by purchase from selling things.