Marine first aid kits are really quite comprehensive and are based on the needs of what time duration you expect before intervention by medical professionals. I spend a huge amount of time traveling by boat trans ocean and a few times have had to use these kits for major injuries i.e. broken bones, medical stapler and large lacerations and I managed to get a third degree burn in an engine-room when I was younger. Often times we have to buy kits based on an indefinite period with the lack of medical help as we can be offshore for weeks at a time. Below is an example of a medium sized kit and you can click around that site for examples. If you decide to build the kit yourself I HIGHLY recommend a "sam" splint some quick clot and a medical stapler.
This kit is from west marine.com. just a starting point and very friendly website