My eonon has the mini usb on the front too.
Whenever I want to use a thumb drive or flash card with a usb adapter, I just run a usb extension cable from the face down to one of the cupholders... when I get out of the truck I can unplug the cable & hide it away in the center console.
Similar thing could be done if you have rear mounted usb port like my pioneer... I ran a cable from the back of the head unit down to the console where I can use my usb card readers or thumb drives.
Most dvd units have a parking brake wire that has to be connected either to ground or to +12v for the dvd portion of the screen to work.
The camera input has a trigger wire as well, I forget if it's a ground or power, but I simply added one of those small red button switches above my hvac controls so I can flip the cam on whenever needed. It may work independent of the dvd function depending on the head unit.
There's always the "don't watch dvd's while driving" which is why the parking brake wire must be connected (or bypassed). I don't suggest anyone ever try to watch a dvd while driving, but if you were listening to a live concert dvd, that might be ok as long as you don't try to watch what's going on unsure:
Comes in handy if there's a hot chick in the car behind me that I'd like to take a closer look at

HA!
Now for cameras... you could spend $150 on a fancy backup camera but that's nuttier than a port-a-potty at a peanut factory.
I got a cheapie infrared backup camera on evilBay for like $15, wired it up, adjusted it & it's been working fine ever since. :thumbsup:
Don't think I have any pics of the camera mounted up, but it's just a waterproof small camera with 6 or 9 IR emitters for nightvision. It's probably 1 1/2" wide by 1" tall. I modded my license plate trim to hold the camera... I need to get some pics of that sucker