For me, it seems that part (or all) of my items get invisible, that's probably what happened if it isn't a bug of my own.
Or it probably fell somewhere a few blocks lower, probably in a spot that is hard to see.
i have the same problem when i die im usually running from endermen and this one time i was sleeping in my bed and when i woke up a freaking endermen was there and when i died i respawned and for whatever reson it spawned me at my origonal spawnpoint and its a 1 minute walk from there and when i went back in my house the endermen was still there i went in killed the endermen looked in my inventory after the battle my itmes where not in my inventory i looked everywhere in the dungen thats literatly right undermy house my itmes were not there i checked everery where around my house and i mean EVERYWHERE but just could not find my itmes well exept the cooblestone but thats all i found this happened in 1.2.4 by the way.
well this one time i died and literatly my diamond picaxe was 10 blocks from where i died and it was right beside a lavafall ok say that diamondpicaxe was the 1 i had ok so imagine this thats how close it was
items do get destroyed by creepers explosions sometimes, also by lava..and cacti
personally im using the death chest mod, all my items get stored in a chest next to where i died, however, if i died by a creeper, the explosion will destroy my chest,but the items stay on the floor for the next 5 minutes