Put it on your bag for school, (:
I just found all of the stuff around my house,
I'm sure you could too.
Draw a dot on an edge in the centre of the Lego piece.
Get the smallest drillbit you have and drill through the dot that you drew.
Open a split ring with the pliers and thread through the hole you've just drilled.
Put the chain through the open split ring and close it with the pliers.
Thread the keyring through the chain and you're done!