Triscuits with salami and American cheese.
This is my first LD so I’m going to keep it very simple. Tetris variant. Portrait orientation, narrow screen. The advancing wall of doom is a grid of blocks moving downward. The blocks compose individual shapes of (probably) four blocks each. Your job is to create interesting combinations of shapes, perhaps just rectangles. Completing a combination removes the lowest corresponding blocks from the advancing wall. When the wall hits bottom, game over. Points for creating shapes.