a pair of binoculars
a pair of tweezers
an elephant call.
First you call the elephants. Then, when they are close but not too close, you look at them with the binoculars backwards. Remember, backwards. That way they will be very small. Then, you pick them up one by one with the tweezers, and put them in the jar.
Don't forget to cork the jar.
Don't have an elephant call? You can make one yourself with spare medical supplies laying around the house:
Awesome! But then, elephants get too small for turning into sandwiches.