From my own personal experience, the hands and ears are the first to mummify -- you almost always see mummification of ears and hands. If the person is barefoot (I didn't have many cases of that in my own experience) the feet also mummify rather quickly, toes first. Ears and hands have low mass and low moisture content to begin with, plus a high high surface-to-mass and surface-to-air ratio, so they mummify readily. Particularly if conditions are rather dry and the person not very fat, you will also commonly see mummification of skin on the facial area early on , particularly of the skin covering the forehead, cheekbones and neck.
I can't remember any case I saw in former Yugoslavia where the hands and ears were not at least somewhat mummified (excepting military personnel wearing helmets -- their ears didn't mummify so fast).
There is not so much air flow over the crotch area (think about it), and it also has a higher moisture and fat content, so it doesn't mummify very quickly. Internal organs are not prone to mummification, in my own humble experience. Neither is the brain.
Also, in females, there is easy access to mucous membranes in the crotch area, which is particularly attractive to flies (the first stage of blow fly maggots primarily feeds on mucous membranes) -- and anyone who knows anything about female anatomy knows there's a long trail of mucous membranes from the genital opening up to the cervix for the maggots to feed upon. Anyway, I'm sure these guys have much more experience with partially mummified bodies than I. It's fairly common for the face and extremities to mummify if the body is left in the open. (But NOT if the body is in an enclosed space, such as the RV storage compartment, as Dusek suggested. Mummification requires lots of air flow.)
Also, have a look at my post #973 and CAPPSMADNESS' post #991 on this thread.