Because I have had two horses colic in the past, I have a 12cc syringe of banamine I keep and if I haven't used it come spring when the vet comes out to do spring time check ups and coggins, then I get a new syringe to put back in the frig. I also have on hand, as again, I have had my QH mare come up lame or my other two do something that I needed bute for. I now have a brand new bottle sitting in the house for those "just in case" times.
My vet and I have a very good relationship. I do call them before I do anything, I ask if what I want to do is correct and I am very fortunate that I can call them out for things if I need them to. I have worked as a vet tech, I am a licensed EMT and a clinical tech so I can and know how to do shots and/or pull blood if needed. Do I like to? No. I would much rather work on a human.