Potions and provisions (food (increase max) & drinks (increase regen)) are two different things. So you could have a food or drink buff and during that then take a potion, however you cannot have a food and drink buff active at the same time.

What you need to be aware of though is that when a buff has a name (brutality, endurance, savagery etc), these cannot be stacked by any means. So for example if you're using a skill which gives major brutality for 20 seconds, using a potion during that time which gives this buff will not give any further benefit.

You can create what it's called as "tri-pots" which are potions that have three buffs to them. So you could take a drink to increase stamina and health regeneration and then a potion during that time which has both of these traits, to increase them further for a limited time.

Here's an idea of what can be created:
http://tamrieljournal.com/list-of-useful-potions-and-alchemy-reagents-in-eso/

Well the question is already answered above, I would just like to add this: Psijic Ambrocia
It's a drink, commonly called a potion, and can be used with food or another drink ..and potions too.

It only provides higher xp gain, so they allow us to stack this with whatever other buffs we usually run with