The cardboard box is a staple of the Metal Gear series, first premiering in Metal Gear in 1987, it functioned as a way to hide the Solid Snake from patrolling guards and cameras. In Metal Gear Solid and Metal Gear Solid 2, the box can also be used as a form of travel. If the player hops on a truck, or a conveyor belt, they will be taken to whatever location is printed on the box.
The box is not as effective if the box and the surrounding location do not match, or if the alert is on. Either of these conditions causes the guards to become suspicious and investigate it, often removing it from Snake. If worn in the rain the box will decay and eventually become useless. In Guns of the Patriots, the card box is featured along with a new item that features similar functions, the drum can. In Metal Gear Online the box can be used, but probably its more useful function is that it deactivates auto-aiming when the player equips it. Metal Gear Portable Ops features the box as a hiding place for team-mates while the player selected character is on the field. Also, to recruit other soldiers, the unconscious guard must be dragged to the box and then phone in a specific frequency.
While most cardboard boxes are simply boxes, Metal Gear Solid: Peace Walker introduced different types of boxes that served different purposes. Some are simple, like a double long box that can hold two people. Others, are more elaborate. The tank box is probably the most elaborate, as it is a functioning tank in the sense that it can shoot. However, it is still made out of cardboard, and does not provide much in the way of armor.
The box has also had cameo appearances in other games, such as Super Smash Bros. Brawl. During a match, the box can be used with Snake's taunt, but it can also be picked up and thrown by opponents to do minor damage. Additionally, It can be unlocked as a collectible trophy.