At the very least, I would take them to the post office & make sure they're sent certified mail so you know they got there. They'll weigh them & tell you proper stamp requirements as well.
I sent all mine through priority. I also enclosed all the applications mateiral into a yellow envelope with my name, AMCAS ID (if they wanted one), and anything other relevant information. I also put a notice on the front of many SMP applications that I will be taking the April MCAT as well.