David Blaine finds a crushed, empty soda can. He holds it in his hands and the can visibly uncrushes. Blaine then shows that the can is not only repaired, but it has also resealed itself. He pops open the can and pours out soda.
This effect works with any soda can and requires two small gimmicks.
The first gimmick is a simple bent paperclip. A bent paperclip can be inserted under the tab of a soda can and used to pull the tab back to "sealed" position. This is exactly what Blaine does when he picks up the can, using a little misdirection and a paperclip painfully hidden behind his thumbnail.
Refilling the can is even easier. A tiny cartridge of compressed carbon dioxide with a needle valve is hidden in Blaine's sleeve, as is a water balloon filled with flat soda. Under cover of his hand, Blaine punctures the can with the valve needle and triggers the device, forcing gas and soda into the can, reinflating it. When the can is full, he shuts the valve off, "opens" the can, and shows the soda's miraculous resurrection!
One important note, Blaine is always careful to puncture the can near the top. If he puts a hole in the can near the bottom, all the soda will come shooting out again when he takes the needle out. That would be bad.
Note: It is rumored that Criss Angel is working on a similar method to seemingly resurrect a dead cat.