A French horn (in a case). Which I dropped. And it rolled down the hill. A long ways down the hill.

I learned two things from that:
1. Never off-road with a French horn.
2. Junior high kids should not be trusted with expensive instruments.

I've also carried, in conjunction with a friend, a full sized christmas tree. We each grabbed a branch on either side, found a balance point, picked it up, and rode one handed side by side down the street with the tree hanging between us.