Ug...so discouraging. My roommate and I made an expedition to go caving. Found a small pocket of monsters that had gold, diamonds, everything. I was on a sniping perch, picking them off until a skeleton hit me and I fell to my death. I found my way back and sacrificed myself to blow up the Creeper to kill the five or six new monsters that had spawned. We thought the coast was clear, so my roommate went in and blocked himself off so he could get my stuff from the first death. Then a zombie snuck up behind him somehow and killed him.
Add that to my roommate taking a swim in lava and all in all, we lost 3 or 4 diamond pick axes, 40+ iron ore, probably some gold, 2 minecarts, diamond shovel, a couple swords, a bow and two stacks of arrows, and miscellaneous other stuff.
Yeah, we're done playing for tonight.
I feel your pain, a slider knocked me into a 1x2 hole with lava at the bottom, I lost two stacks of iron, some gold and my tools and what not. Thankfully though it was at the start of my day and I made it all back and then some, after the shared map I'm going to start on my 1km long rail track.