This free PDF download from the World Health Organization (WHO) details common medicines and their uses. It's not something to play doctor with (leave that to the professionals), but it should provide an overview of popular drugs should access to medical advice be limited.
We at Gun Digest are not doctors, but there are plenty at WHO. We trust that this information is accurate to the extent that we trust WHO. Depending on how much value you put into that organization's views, this should be of benefit to you. Here's the source site.
Click here to download the WHO Model List of Essential Medicines, print it off and keep it in a secure place.
P.S. Here's another download just for children's medicine.