Stock FPSC does not support non-weapon inventory. You can however use the 1-9 keys to directly select weapons for items.
It sounds more complicated than it is: You have to create a weapon that uses a hud thats not in the upper right corner but simply goes accross the whole screen (more or less) and consists of a piece of paper, a map, an LCD display or whatever. So when the player selects the "weapon" he can read the info from the "hud".
To make it a little more elaborate you can make the "item" be destroyed when its no longer needed (code used to open door etc.) to make room for more "items"
OR you check out The "RPG Mod" by Olive Tree Games ---->
http://forum.thegamecreators.com/?m=forum_view&t=154325&b=21
In case you find my grammar and spelling weird ---> native German speaker ^^