Suggestions is simple as it sounds:
For Skeletal Wyverns remove Saradomin Armour and replace it with skilling supplies and alchables.
For Hellhound remove Zamorak Armour and replace it with skilling supplies and alchables.
For Gargoyle remove Guthix Armour and replace it with skilling supplies and alchables.
For Bloodveld to drop Blood Runes as it is original drop being famous for.
For Chaos Druid to drop all sort of herbs(higher than irit herbs less common) and be aggressive to any level.
For Chaos Dwarf to have any sort of drop table, cause they're one of NPCs not worth killing at all.
For Jellies/Trolls to remove Granite replace with Rune Items instead. Granite should be exclusive to Gargoyles only.
For Dagganoth Kings make Dagganoth bones one at a time or noted all three.
For Poison Spider to have a 50 red spider eggs noted drop 1/1000.
For Obsidian Dragon to drop noted both hides(trip takes up to 7 - 9 kills depending if you get stacks or items worth something)
^Otto mentioned this before, So I bring this up again.
For Chaos Elemental to drop Rune Essence more common than Yew/Magic Logs. Also, remove Comp bows as they are useless on drop table and should be move to(easy, medium, hard) clue rewards.
Not sure if its so difficult to change dropped items on certain npcs but it might turn useful tho.