I have 5 gallons of drywall primer, would this be okay to use on the wood trim also? Please help?

Most certain it is a latex based primer. You can use it where ever you need to prime, if you are not covering stains specifically. Yes you can use it on rocks and any masonry products like plaster. The difference between regular primer and that, is the regular has more pigment and I think Titanium in the formula. That is what covers the stains. Drywall primer only has to seal the outer paper on the drywall,because most painters or DIYer's will cover the drywall anyways. Go for it! Can't beat the price! Byee, hoped I was able to clarify things a little for you.