I've made a quick sketch today. This is one version of how the basic HUD-items position could look like:



We would have the action panel in the upper part of the screen, exit-key indicator (key would appear when collected), number of currently collected bonus items, currently held object & potion inventory (displaying one currently selected potion, one previous & one following potion in the inventory).

Player would carry only one object at the time & switch it with other object in the level with action button. Potion button would switch through 2 potions in the second level & 10 potions at the last level, always displaying only up to 3 potions in the HUD.

How does this concept seems?

We could use the action & potion button pressed together as a trigger for potion consumption or use separate button for consumption?