Basically it's a kit with supplies to handle any emergencies that come up. Off the top of my head some good things to have around are corrid, calcium citrate + d3 tablets, neosporin triple antibiotic without pain relief (very important for it to have no pain relief as the pain reliever used is toxic to chickens), gauze, petroleum jelly, Epsom salt, syringes and perhaps a tube feeding kit. All good stuff to have around if a bird gets injured or sick. There's other good stuff to add too, so just take my list as a good starting point