I'd also make them use a minor action in order to grab the potion from their packs. =)
...but those potions also tend to get knocked loose or break when being struck at.
Drinking a potion doesn't incur an opportunity attack. Drink next to the orc and then spit in his face for a free action.
That's a nice house rule. How do you break them, though? When the NPC crtits or the PC rolls a 1 (is there slang for that? Wiff, maybe?)

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.