You could start with on off the shelf kit like AMKs .9 Ultralight and then customize to your needs and to that of your companions. I just posted my own FAK in another thread and my emphasis is on tayloring to suit my needs.

Kits are one thing, training is another. "The more you know, the less you carry." - Mors Kochanski. I have some Wilderness First Responder training but unfortunately I haven't renewed. I will probably just get WFA cert. for my next go around. With training AND experience, you will know what makes the best kit for your own needs and activities. But if you or your companions don't have FA training then a small simple off-the shelf kit is your best bet. Carrying something you don't know how to use is just dead weight.