Add this in at the beginning:
C=0
FOR I=1 TO LEN(INV[])-1
INC C,INV[I]
NEXT
IF C==0 THEN ?"Nothing in your inventory."
So that it shows a message when your inv is empty.
Add this in instead of ?"1-WOOD :";blahblah[blah]
IF INV[1]>0 THEN ?"1-WOOD :"INV[1]
so that it only shows up when you have anything of that material.