All you have to do is use the Hypnotize Big Daddy Plasmid on a Big Daddy so that he thinks you're a Little Sister and protects you. In order to do this, you need the Hypnotize Big Daddy Plasmid and the Natural Camouflage Tonic. After a few hits, between 1-3 health packs should lie on the floor for you to grab, for free. While you can buy health packs at health stations for $10, you can get them for free by simply smashing the machines with your wrench.
