You do realise that this is poor design? I have to admit that I do this too, especially when you need mana to solve an out-of-battle puzzle, but a well designed game shouldn't make the player 'cheat' the game in order to progress.
I can't say I've had any issue with health/mana in battle/dungeons yet, though I have only just reached Al Mamoon, so maybe it becomes more of an issue later on.
At the moment, if I'm getting low I'll get into a battle and get the enemies down to one, then just run around for a while (switching between familiars/Oliver as need be). Drippy throws out green and blue glims at a fairly regular pace, so I just run around 'til he does and collect a few. Sure, it takes a few minutes every now and then, but it's a good way to top up for free, and I've not yet used a single mana item. Does he stop doing this later in the game?