It wan't really a real inventory system, it was just icons with a count that reads a variable, then when you pick an item up it adds to the variable and when you use it it takes away from the variable. The icons for the items were in a fixed position. It's just a matter of positioning the icons and the text and setting the text to display a number from the variable, it's fairly basic.
I'm not at the PC for a few days, but when i am i'll see if i can do a quick example script and post it for you. Bare in mind though that it might take a while for me to get to it because i'm pretty much finished with GameGuru once i release my Egyptian isometric kit and i'm pretty busy taking Unity courses.
If you want a better inventory system, Smallg did a really good system and posted it in his pinned thread here.
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