In our game SURVIVOR, I left the main menu design and programming to the last few hours. The menu consists of 3 buttons (Next Level, Previous Level and Play). After laying out the buttons, I discovered that they are not working and do not respond to mouse clicks. I think the error was due to the pixel perfect camera but I had no time to debug. Therefore, I added 3 lines of code to do the button function by keyboard presses (Left, Right and Space) then changed the text on the play button from "Play" to "Press Space to Play". I then assumed that I never planned to add clickable buttons to the menu (the button are still there just for cosmetics :D).
We also had a hedgehog-like enemy which I wanted to give a rolling attack or spine melee attack but I didn't want to animate any of those. So I changed my mind and made it use the same bullet attack I was making for the cannon enemy and assumed that they are gun-armed hedgehogs.
The only other hack I always use in any jam (which seems to be pretty common) is the large singleton class "GameManager". Any info that needs to be known by everything is there. It is also responsible for all of the sound effects (except jumping which I dirtily embedded into the character controller). I know that this is a horrible programming practice but tight deadlines always wins over code cleanness every single jam.