An appropriate medical kit should be durable, padded, weatherproof, and easy to carry.1
If you carry medications, include a weatherproof/laminated drug-treatment card for each medication, since a wide variety of practitioners may end up using the same kit. These cards should include: (a) correct pediatric and adult doses for specific conditions, (b) information on how to reconstitute (if a powder) and administer the medication, and (c) contraindications and adverse effects.
A "one-man mobile forward clinic" consists of a clinician carrying a backpack with a complete basic life support kit and simple surgical instruments. "In skilled hands and with support from the local population, the one-man mobile forward clinic may handle close to 80% of all casualties."2
Dr. Matthew Lewin, who equips scientific teams for remote expeditions, suggests that some of the basics for any kit are: ear plugs, nail clippers, superglue (small wounds), suture stapler (larger wounds), thermometer (to determine if there really is a fever), duct tape (lots of uses), condoms (no need for pregnancy or STDs in the field), pregnancy tests (to know if care must be modified), zip ties (to prevent tampering with the kit, but still allow it to be opened quickly), adrenaline (envenomations and allergic reactions), and antibiotics. For any other medications, use pills rather than capsules, which may crack in an arid environment; even better are vacuum-sealed medications. What he does not include are venom suction extractors (worthless), rehydration salts (use salt and sugar), or unnecessary narcotics (potential for abuse is great).3
The most common situation in which health care professionals may need to provide medical treatment with few resources is while driving. I believe that all advanced health care professionals should carry medical supplies in their vehicle. Not to do so is more than irresponsible: it is a repudiation of the healer's moral codes. (I believe it's unacceptable to hide behind any fear of liability. If your services are gratis and you have no preexisting requirement to intervene, at least in the United States, you are completely protected from liability.)
I follow two rules as to when to stop and ask if help is needed. I stop when (a) people seem to be in distress and no one else seems to be helping or (b) prehospital personnel seem to need help. (A clue to this is when one or more of them is kneeling next to a patient.) I have intubated, performed cricothyrotomies, put in chest tubes, and done other advanced procedures at the roadside over the years. If you don't have these skills, that is no problem. Use what you know, the equipment you carry, and lots of improvisation. It will be appreciated.
The equipment you should carry depends, in part, on the skills and knowledge you have. However, in lifesaving situations, you do not want to be missing key equipment that you may need. Note that this ...