i would disagree with the statment that pre-made kits are no good.
seaside pharmacy in california has been making some very heavy duty medical kits for over 100 years. In fact if you have a documented boat they will provide almost all needed prescription drugs including some pretty heavy duty pain killers (toridol injectable) and antibiotics.
i have had one trauma doctor and one trauma surgeon go through the kit they made for me and they had nothing to add.
i would suggest you contact them and tell them where you are going and they will make the appropriate kit.