For young geeklings, you can make a fun Tetris puzzle out of a sandwich in a few easy steps.
Step 1: Step 1: Make a Sandwich
I would recommend a sandwich made of solid bits (Ham, Turkey, Cheese) rather than PB&J.
Step 2: Step 2: Score the Sandwich
Get a bread knife, and cut a series of shallow lines in the top of the bread. Make three equidistant horizontal lines by bisecting the bread, then bisecting the two remaining halves. Then, do the same thing with vertical lines (one in the center, then one on either side).
Step 3: Step 3: Cut Out Your Pieces
Keep in mind what the Tetris pieces look like as you cut the sandwiches. The T, the S, the L, and the long bar. You won't be able to make the puzzle out of all of them, but you can get most in a single sandwich.
Step 4: Step 4: Wrap the Results
Turn over the sandwich pieces to avoid showing the scoring, then place the results on a plate so that they are no longer in place. Then cover the plate with plastic wrap to keep the pieces in place. Now it's ready to put in your geeklet's lunchbag.
Make sure to tell them to play with their food!