Placing in a ziploc (squeeze the air out each time you close it), may help with storage.

Save some RX vials, or buy some extra at the pharmacy for
smaller portions (whose stock bottle is in a ziploc). These have caps designed to minimize humidity and air (but they are not perfect).

We have only had 2 things go bad: generic magnesium chloride 64 and a bottle of St. John's wort years ago. ( I can't remember this company at the moment..but Solaray keeps coming to mind).

Vitamin C will discolor to warn you that is is oxidized.
A hint today, is that the company may put a "do not eat" thingey in its product, suggesting moisture damage potential. This is a message to you to carefully store that product. Our MegaRed now comes with one of these in each bottle.

Really sensitive things now come blister packaged like SAMe which is really unstable to air and moisture. Many OTC drugs are now blister packaged this way (except large quantities like sold at Costco and Sam's club.)