There is a small problem with all of these answers: they are slightly incorrect.
When you die, Lava and exploding creepers may destroy some or all of your items immediately. The rest are scattered on the ground around you, and a five minute timer starts (even while you are on the death screen). This timer counts down as long as the chunk the item is in remains loaded into memory.
For performance reasons, approximately a 20x20 block of chunks around the player are loaded into memory at one time (about 320x320 blocks, with you in the center). If your bed/spawn is farther than 160 blocks away, then the timer on those fallen items pauses when you respawn, and it will not begin again until you get within 10 chunks and the area they are in is reloaded into memory.
In single player, this means that the items will almost certainly survive until you return, as long as you do not dally, regardless of how far away they are. However, in multiplayer you are not the only person in the world... having someone else in the same general area as your fallen items will cause the timer to continue to count down, even if you are very far away.
But this is only for items that are on your person (and thus fall on to the ground when you die); items in chests remain permanently across saves and deaths. If the chest is destroyed they all fall on the ground around the chest, and the same 5 minute timer and rules about the chunk being loaded apply.