One thing that continues to plague me is tool/weapon counts. I've never been able to master this aspect of a mission, so I just take a best guess and hope it works out.
My experience as a blackjacker that finished all but a few missions available though the ingame downloader on difficult:
Most missions are pretty okay at hardest difficulty if using only the blackjack, lockpicks and rope arrows. The spyglass and lamp improve life a lot and there really is no reason to not give them to players. The compass is rather useless in most missions but it also does not hurt giving it to players. Same for the sword - that is also used to finish off knocked out assassination targets (always knock out your targets first to avoid the insult *g*).
When it comes to consumables, i would (on hardest) default to
- three to five broadheads (they are lightweight, cheap and good for remotely triggering actions)
- two water arrows (they are pretty usefull from time to time but look bulky)
- one or two noise makers (for when someone wants to get through with a perfect stealth score - otherwise he could just jump or throw around stuff until the AI starts moving)
- mission-specific stuff like rope arrows or holy water as needed (assume that the player recollects rope arrows after use).
I would also add two odd pieces of equippment, that are not needed or even useless in the mission.
- The flash bomb/mine (pretty useless)
- A moss arrow (convenient sometimes)
- A health potion (nice if rope arrows are scarce and targets are high above ground)
- Another noisemaker
- Another water arrow
- Holy water (useless if there are no undead in the mission)
More broadhead/water/rope/moss/noisemaker arrows could be stored at appropriate spots. Of other equipment one or two to find in the mission are more than enough most of the time. Also don't forget, that the player can reuse his broadheads used for killing AI. And each archer AI provides an additional broadhead.
Gas arrows are only needed if there are elite guards or other unknockable AI. But if you play on hardest some ghosting abilities are expected - so if the elite guards are easily avoidable there is no need to hide more than the odd gas arrow in the alchemist's workshop.
The loadout at start and what can be found in the map should obviously be more generous for medium and easy difficulties...