Brain + ethanol experiment suggestions needed
The main problem with what you are asking is that you want to show effects on vigilance and memory in vitro. That is just not possible: if you want vigilance and memory you need a live animal, there is no way around it.

Next point: you have an audience of non scientists, so you can lose them very quickly if you start speaking about NMDA, LTP or similar things without a clear explanation, so start with that: get a nice review (Pubmed is a good start, as always), and give a simple theoretical explanation of one of the mechanisms involved. It is then important to clearly explain the experiment you will perform, and what you are expecting to see in case there is an effect.

Unfortunately the best way to see effects on NMDA receptors would be electrophysiology. This is not trivial and, if you have never done it, I would not suggest going that way. However, if you have access to an electrophysiology setup you will most likely have access to someone who uses it, and that could make the experiment for you.

I am not an expert on this topic, but a quick research on Pubmed seems to indicate that alcohol can, for instance, reduce LTP in hippocampal neuron.
Maybe what you could do is having someone patch hippocampal neurons and show how an LTP protocol is used. You don't necessary have to show them the whole thing (I doubt anyone in a right state of mind would bare to stay until the whole experiment is performed in control condition first, and alcohol later...).

Also, the results of these experiments are often non obvious to analyse, so you should have some data prepared and analysed earlier and quickly show how analysis is performed, before showing the final results.

Calcium imaging experiments could also be used and would probably give results that are easier to understand for a laymen audience.

See for instance Fig. 1 or Fig. 5 of this paper (just the first one I found, there surely are other):
Ethanol alters calcium signaling in axonal growth cones.