When racing on the sailboat, when (not if) I injure myself, I use duct tape and folded paper towels until I can reasonably dress the wound.
We started our RV first aid kit with a purchased kit, removed most of the unneeded packaging, and added items that we really needed. We frequently travel in rural third world countries, so we are well inoculated and carry medicines for lower GI issues, but do carry remedies for that. Have a chat with your physician for recommendations.
I look at our kit as a quick response to stop/control bleeding, prevent infections, and rely on our ability to get to real medical care to resolve major trauma.