To answer the category stuff:
For long-distance, road-biased driving in cool - warm conditions - Merrels or vellies
For warm-to-hot conditions where snakes, scorpions etc. are not an issue, but might have to get in a puddle or mud - TEVA or Rocky style sandals (I hesitate to call them sandals - they're way tougher than that).
For heavy rocky terrain, ala Road to Hell in Richtersveld, or where extra foot protection is needed - light-weight walking boots with a decent Vibram sole
Actually - the Vibram sole is pretty key to all of it I think - wears well, chemical-resistant and usually excellent grip.
Basically any shoe that requires minimum care for maximum foot protection and that is environment-specific ito temperature, breath-ability and wade-ability.
I walked miles and miles and miles in vellies (and endured combat contacts too) and they were awesome - and at the price you can bin them when done.
Cheers