Welcome to Part 4 of my Four Part Series on Shrink Item, a Dungeons and Dragons spell that can be as dangerous to the caster as it is fun to use on others. Here are some of the risks to look out for, as well as some of the ways that your DM might want to scale back, so to speak, your grand Shrink Item extravagances.
Anti-magic. It's not beauty that's in the eye of that beholder, but doom! One glance from that anti-magic ray, and every shrunken item on you suddenly pops back to true size! While you can hope that the gallons of acid will put out the campfires, and the falling iron plates will splash away the acid, and the ogre corpse will cushion those falling plates, things just might not break that sweetly for you. What will you do, then, when the beholder takes a look, or the enemy mage casts Dispel Magic, or you step into that anti-magic zone? Maybe the best answer to this dilemma is keeping your shrunk items in a Bag of Holding, Handy Haversack, or Secret Chest. They'll be inaccessible in an anti-magic zone, but far away and safe in their non-dimensional space, at least they won't be unshrinking!
Tossing your cookies. What if your DM says that when you take a tumble, falling more than 5 feet, say, there's a chance your shrunk items will activate? They "think" they've been "tossed" onto a solid surface. Yet another reason to get that Bag of Holding!
The true meaning of volume. Does the volume of an empty box include the empty space inside the box? Your DM may say that a pillbox made of six 10ft x 10ft x 1/4in plates actually has a volume of 10ft x 10ft x 10ft ... 1,000 cubic feet rather than a mere 12. You may have to reconcile yourself to modding the map with walls, terrain (horizontal plates covered with caltrops, say), and maybe blinds. You can make a blind with two plates, joined with a right angle and pierced with arrow slits -- it's not a pillbox, but it does offer improved cover from one or two directions, anyway.
Tin Foiled! In the Mod the Map part of this series, I suggest constructing objects from 1/4-inch thick steel plates. That seemed reasonable to me from a real-world point of view ... a quarter-inch thick steel plate sounds plenty sturdy to me. But check out pages 60-61 in the Dungeon Master's Guide. A five-foot section of 3-inch-thick iron wall has hardness 10 and 90 hit points. A 2-inch-thick iron door has hardness 10 and 60 hit points. Stands to reason a 1-inch-thick plate would have 30 hp; half an inch, 15 hp; quarter inch, 7 hp. That means any foe can punch a hole in your steel plate by inflicting a measly 17 hp. If your foe has admantine weapons, it ignores hardness and only has to inflict 7 hp! An easy DM strategy vs. thin iron structures is to knock holes in them! The solution may be to limit yourself to 1-inch-thick plates, since a generous 30 hp is hard to punch through. Your available square footage drops substantially, though: Roughly speaking, a 5x5 plate is 2 cubic feet, a 7x7 plate is 4 cubic feet, and a 10x10 plate is 8 cubic feet (once you cut out the arrow slits).
How to unshrink. How do you unshrink items, exactly? What does "tossing onto a solid surface" mean? Is "tossing" the same as "dropping," and what if your DM says that "tossing" is a move action? Or a standard action? When you "toss" something, can you specify orientation? And how does unshrinking with a command word work? Do you have to be touching the item when you utter the command word? If not, what is the range on speaking the command? Casting dispel magic may be your best way to unshrink items from a distance.
A spell as good as Shrink Item may well bend or break the balance of power when put to all the uses I've imagined for it. Given that the spell has no reputation as a game breaker, it may be that few players have thought to explore its full potential. Or it may not really be that potent after all. Either way, be open to any rules interpretations your DM may suggest. Certainly, no use should inflict more than 1d6/level, with a reflex save for half, max 10d6. If used to channel or confine, a reflex save might be called for. Be open to game balance adjustments -- after all, even fully nerfed, Shrink Item remains a sweet sweet spell!