Never got rules for construction in 4e, so I couldn't use it:
Cloak-plus-hood made of skunk pelts (trophy from the character's first adventure) with a tail attached on top of hood, can squirt you with a Troglodyte-like Odoriferous Aura that bothers only your enemies.
Message a spy looking in through the window at you, "I can see you out there."
I Illusion'ed my Ranger/Rogue (Arcane Trickster) to look like the bad guys' Executive Officer, walked into the Boss' office with the rest of my 'captured' group in tow, and started a 'who's in charge?' quarrel with him. When the Illusion came down was the group's signal to attack.
Pour a Potion of Gaseous Form down somebody else's throat and tell him he is going to fade away into nothing but mist forever, unless he tells you his secret.
Facing an Ice / Snow Monster? Light a candle, smash it down on an arrowhead, and ask the DM if you can do Fire damage to the monster.
Jump into a 30-foot-deep lake wearing Plate Metal armor ... and a Rope tied around your chestplate. (Make sure the strong guy has a tight grip on the other end!)