Glass:
I believe crude lenses can be made by pressing molten glass into a curved mould (which I think can be made of clay or similar).
So what the average person can do is explain that the curved glass has optical effects which a glass-maker of the day can test and demonstrate - and that point the glass-making technology of the era determines how useful the knowledge it. I suspect it's probably already quite well known to the limits of the glass-making technique of the day so you've actually added nothing.
What knowledge of lenses needs is the application of the scientific principle to the investigation and documentation of the effects.

Floating liquid glass on mercury to make flat sheets is something that can be explained very easily, but I have no idea how easy it will be to get hold of mercury in sufficient quantities.

Mentioning that clearer glass can be (possibly) made by adding a small quantity of lead might encourage glassmakers to try (and possibly succeed) but I think that is the limit of most people's knowledge.

Porcelain:
I agree with Peelee here - my mother knew how to make porcelain (I think) - but then she used to be a potter, I don't know, and more to the point I wouldn't know how to identify the needed clays even if I did.

Gunpowder:
From what I have read the method of mixing is actually very important to the quality of the end result. However, yes as everyone (or nearly everyone) knows one can extract saltpetre from bat guano - but who knows how? I think it takes the form of colourless crystals, but one needs to know more than that. Probably more useful knowledge (as bat guano is only available in quantity in a few places) is that there will also be lots in old middens etc., but I suspect most people would fail to make anything useful here unless they have already practiced making in this world.

Penicillin etc.:
Unless you know a lot more than a common person all you get back to here is mouldy bread poultices.
More useful on the medical front is the use of cowpox for smallpox vaccination.
I know the basic principle behind extracting vaccines from blood - but who has any idea which part of the blood is needed once separated? (Or how much?)

Construction:
Now we might be getting somewhere. The "Roman Arch" (semi-circular) was used for centuries before people realised that gothic (pointed) arches would also bear loads quite well. I may not have the maths to describe how, but by demonstrating that they work I could enable the architects of the day to work out the maths and have a lot more flexibility in building construction.
No - I have no idea how to make concrete, other than to ask ancient Roman engineers who did know how.