As part of volunteer work with refugees, we have found that families need to carry a couple of sandwiches for their travel to sponsoring relatives in the U.S., after release from detention. These sandwiches get crushed in their paper bags, and so I made up cardboard boxes from soft drink packages.
This box will hold two or three sandwiches, and is reclosable. You can easily get two such boxes out of one 12-pack, if the box is opened from the middle, preserving the two closed ends.
I have one 12-pack soft drink box, a sharp knife (although you might want to use scissors for safety), and a gift card for measurement.
Step 1: Mark the Box for the Desired Height
Using a gift card, I mark the box to define the height of my sandwich box. You may, of course, use any height that you find convenient.
I pierce the corner of the box with the knife to mark the height, but a pen mark would be fine, as well. Do this for all four corners.
Step 2: Cut the Edges of the Box to the Marked Height.
Using a knife, cut the box edges down to the marked height, creating four flaps. Scissors are probably safer.
Step 3: Fold Back the Flaps
Carefully fold back the four flaps, creating a crease to define the top of the sandwich box.
Step 4: Trim the Flaps to the Size of the Box
After creasing the flaps, fold them over the box, one by one.
Measure them against the width of the box, and trim them to the proper length.
Step 5: Set Up to Cut Your Locking Tab
Fold down two opposite flaps, to act as the 'inner' flaps of the box.
Next, fold down the two remaining flaps, which are the locking 'outer' flaps.
Step 6: Cut the Locking Tab
About 1 inch from the end of an outer flap, cut a tab, pointing inward, as shown.
If it is too close to the end, it might tear out, but an inch seems to work out well.
Step 7: Mark the Location of the Slot
Fold the flap with the locking tab over the opposite flap.
Using a knife or pen, mark the ends of the tab, to define the width of the slot that the tab will lock into.
Step 8: Cut the Locking Slot
Make a straight cut between the two marks that define the location of the locking tab. This is the slot that the tab inserts into.
A single cut is sufficient, but you might trim this slot a bit to make the tab more easily insert into it. I usually find this unnecessary, after the tab has been inserted once.
Step 9: Close the Sandwich Box
Fold down the inner flaps
Fold down the outer flaps, slotted flap first.
Insert the tab into the slot, and then press the flap down. The tab will keep the box closed!