Open a single side of the box and remove tissues. (You will need them in a later step)
Step 1: The Inside
Cut the bottom off of a DIFFERENT tissue box.
Step 2: "flaps"
Open one side of the box you tore the bottom off and rip off the two "flaps".
Step 3: Taping
Bend the flaps in half so they make a right angle, then tape them to the box bottom you cut off. Make sure they are far to one side so you can put in the object you are hiding, and also make sure the brown side is not the side you tape the flaps on.
Step 4: Building
Put the the flap side down in the open box (the one you haven't destroyed).
Step 5: More Tape :/
Tape the small flap to the flap you taped onto the bottom part of the box. Put the tissues in, then open the other side and do the same.
Step 6: Disguising
Pull one tissue out so it looks normal, add your treasures and seal it up with ONE piece of clear tape. To open it, just take off the tape.