Years ago I used a period Pharmacopoeia Formulary book, that included details of what form and appearance each respective medicine was suspose to looked like, and in what form it generally came in.
Also had a couple friends that were pharmacutical chemists helped a bunch too. Will have to do some digging to find my old research lists for it. To see if it might add further fodder.

In most cases where where the product was in a crystalline (a salt) form, one could use Salt (Sodium Choride), Alum, Citric Acid, Epsoms Salt, or Rock Salt, depending on how fine or course grained the original product was. I generally avoided anything sugar based since it tends to rapidly absorb any residual moisture and can turn into a solidified brick in your jars. Most of the salts can sometimes clump up but you can generally shake them loose again.

Powders. One could use Cream of Tarter, Baking Soda, Corn Starch, etc for starters. If memory serves correctly raw form Opium was a fine black powder. For this I used dehydrated activated charcoal.

Herbal items one can generally find a close match going through the spice/herb racks

If one is making items in pill form it gets a bit tricky sometimes. Most times one can use flour made into a stiff dough, can add food color if the product had a particular color hue desired, roll/form into pill sizes you need and let dry. They tend to hold up fairly well. I still have some that have been in jars 20+ years and still look like the day I dumped it in them.

Recommend avoiding any product that is or could be caustic, volitile or reactive in itself, or to anything else present, if something were to break or spill in transit. Also caution on products that could freeze and rupture the given container, if displayed or stored in areas subject to possible freezing temps. These items mentioned intended solely for static display purposes only. I had other items I used for demonstrations, sick calls and surgical demos.