Which baby medications and other medicine cabinet items should I have in the house?

A very short list! You need only a small number of things-- most of the stuff suggested on those long lists from the "baby stores" is unnecessary. I rec generics of: Acetaminophen (or Ibuprofen if past 6 mos), diphendydramine (benadryl), salt water nose drops, and an inexpensive digital thermometer. Have the phone # of a 24-hour pharmacy written down if you ever need it.
Fever reducer is #1. One important medication is to have a fever or pain reducer such as acetaminophen. (ibuprofen is helpful >6mo of age). Benadryl (diphenhydramine) is useful for allergic reactions. Hydrocortizone cream is great for baby eczema or skin rashes. Diaper rash cream (any with "zinc oxide" or even vasoline) & baby wipes. A digital thermometer that can read a rectal temperature is also essential. Hope that helps!