Items will disappear if they are on the ground for 5 minutes after you die.
This timer starts ticking as soon as you die; even on the death screen that timer is going to keep counting, so if you go take a break to grab some food and come back to find out your character's been lying around dead for 10 minutes, your items are gone.
Also, dying in lava or fire will make you lose any items that fall into the flames.
Items that fall onto cactus are also destroyed.
Caveat: if you spawn far enough away from where you died and the chunk becomes unloaded, the item timers will freeze until the chunk is loaded again.
gaming.stackexchange.com/users/207/Mana
As per this question , your inventory will stay around the point where you died for approximately 5 minutes.
If you die with creepers around, be aware that an exploding creeper (after your items have dropped) will probably destroy some/all of them.
From personal experience, sometimes the items kind of spray out around where you died, so do a few laps when you get there to make sure you got everything.
gaming.stackexchange.com/users/816/sjohnston
Just for the purpose of being complete: items that fall into or are thrown into lava are destroyed immediately.
(You can use this to your advantage if you're sick of storing stacks of dirt or something.)
gaming.stackexchange.com/users/304/JavadocMD
Also, if the game crashes while you're on your "body-run" there is a high likelihood that your stuff is gone even well inside the five-minute window.
gaming.stackexchange.com/users/2888/clweeks
Some more info: Items get scattered in an area around you on death, and there is a glitch where they go through walls.
Another glitch makes your corpse pick up the items after they were scattered, and they get destroyed.
I believe these glitches account for the "there's a chance that items get destroyed on death" you read on the forums over and over again.
gaming.stackexchange.com/users/4892/RotHorseKid
Possible Duplicate:  What persists after a respawn in Minecraft?     I've apparently lost my diamond sword due to a death far from my spawn point. Was I just unlucky or do items disappear if you are so far/if they are on the ground for X minutes?
What causes an item to disappear in Minecraft?
gaming.stackexchange.com
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gaming.stackexchange.com/questions/11010
gaming.stackexchange.com/users/3015/Rapida
Items will disappear if they are on the ground for 5 minutes after you die. Items stay around for 5 minutes after death, however they may glitch through walls too.
Users suggest items stay around for 5 minutes after death. They may glitch through walls.