Tutorials
Item_Crate
You will of seen the resupply crates littered around HL2 frequently, the small breakable boxes, and the big chests of ammo.
They are dead simple to add and configure as well.
item_ammo_crate
The wonderous chest of ammo:
First of all select it from the entity list, to do this select the Entity Tool (Shift+E) and place it in your map by clicking in the 3D view with the tool still selected.
Open up the properties (select the chest and press ALT+ENTER) and you will be able to choose various items to fill it with
item_item_crate
The small box of joy:
Add it the same way as the chest, remember this crate has physics appiled to it by default.
A few more properties this time, similar to those found in prop_physics but the main ones are located near the bottom, these control the contents.
Easy peasy
Blink