It seems there's a tonne of unused icons in BG1:
IBOOK68 (History of the Nether Scrolls, currently uses the regular book icon)
CBOOT06 + IBOOT06 (worn out boots, currently uses the boots of grounding icons)
CBRAC11 + IBRAC11 (bracers of binding, currently uses the gauntlets of weapon expertise icons)
CCLCK08 (Algernon's cloak, currently uses the nymph cloak icon)
IHELM06 (a golden horned helmet)
CMISC04 (an old design for Bassilus' holy symbol)
CMISC05 (some kind of tunic)
IMISC08 (silver coins?)
GMISC13 (Samuel's body, currently uses the male body icon)
CMISC14 (a pile of gems)
IMISC1A (bottle of wine from the winepress, currently uses the icon for Landrin's bottle of the wine)
CMISC1B (butter knife of Balduran, currently uses the throwing dagger icon)
CMISC3A (a book of some sort)
CMISC46 + IMISC46 (a pile of treasure)
GMISC62 (dead cat, currently uses the sack icon)
GMISC65 + IMISC65 (Brage's body, currently uses the male body icons)
GMISC66 + IMISC66 (Farmer Brun's son's body, currently uses Samuel's body inventory icon and has no ground icon); I don't think this one is actually used, as MISC67 is Brun's dead son.
GMISC68 + IMISC68 (Abela the Nymph's body, currently uses the child's body icons)
IMISC70 (Delorna's statue, currently uses the Kozah's idol icon)
IMISC71 (Delorna's spellbook, currently uses the regular book icon)
IMISC75 (dagger of venom, currently uses the dagger +3 icon)
IMISC76 (the dream potion, currently uses the antitode icon)
IMISC77 (skull of Kereph, currently uses the regular skull icon)
GMISC92 (switch for an engine, currently uses the sack icon)
GMISC94 (mallet head, currently uses the sack icon)
GMISC95 (mallet handle, currently uses the sack icon)