All these, plus another component I personally enjoy in adventure books -- flawed characters who complement each other, and so become collectively stronger than they stand as individuals. For example, Bigwig has an amazing character arc, where he learns to subordinate his strength to Fiver's vision and Hazel's leadership.

Other examples include the foursome in "The Three Musketeers" (who explicitly arrange their affairs to contribute equitably from among their talents, money, and time), and "Kidnapped" (where David Balfour and Alan Breck have to learn to trust each other in order to negotiate the dangers they face on each other's behalf).