How many things are there in a first aid box?

A household first aid kit should include 16 essential items, according to the provided reference.

Here's a breakdown based on the reference:

• A well-stocked drug store can supply all items for the first aid kit.
• The reference explicitly mentions that a household first aid kit should include 16 items.
• One example item cited is diphenhydramine (Benadryl), an oral antihistamine.