A box of baking soda whose name changes to "completely ineffective baking soda" when it is in a container with something that smells funny.

First to lay some groundwork:

"Shipping Trunk"
A chest is a kind of container. A chest is always openable. A lid is a kind of supporter. A lid is part of every chest.
Before opening a chest when something (called the obstruction) is on a lid which is part of the noun:
   say "Better remove [the obstruction]." instead.
A thing can be innocent or smelly.
The Storage Unit is a room. The shipping trunk is a closed chest in the Storage Unit. The trunk contains some garlic, a loaf of moldy sourdough, a mildewy bathtowel, a pair of unwashed socks, two dead trout, and a box of baking powder. The garlic, trout, sourdough, bathtowel, and socks are smelly. The baking powder is innocent.
The shipping trunk's lid supports a small card. The description of the small card is "'Please, please do not open this trunk.'"
After opening the trunk:
   if the trunk had been open:
      say "You steel yourself...";
      continue the action;
   otherwise:
      say "There roils up from inside an indescribable funk, which, when you can see straight, you have no trouble attributing to the presence of [a list of smelly things in the trunk]. You also note [a list of innocent things in the trunk] in the corner.".

And now, with that preparation:

Before printing the name of the baking powder when the powder is in a container which contains a smelly thing: say "completely ineffective ".
Test me with "open trunk / examine card / get card / open trunk / get powder / inventory".
Test me with "open trunk / examine card / get card / open trunk / get powder / inventory".
Storage Unit
You can see a shipping trunk (closed) here.

>(Testing.)

>[1] open trunk
Better remove the small card.

>[2] examine card
"Please, please do not open this trunk."

>[3] get card
Taken.

>[4] open trunk
There roils up from inside an indescribable funk, which, when you can see straight, you have no trouble attributing to the presence of some garlic, a loaf of moldy sourdough, a mildewy bathtowel, a pair of unwashed socks and two dead trout. You also note a completely ineffective box of baking powder in the corner.

>[5] get powder
Taken.

>[6] inventory
You are carrying:
a box of baking powder
a small card