Here is my Marty, been putting this together for some time. I tried to get it as accurate as possible, without breaking the bank, and with what was available online and in some second hand shops I have been visiting.
Parts so Far...
80s Guess 2 tone jacket (not accurate)
80s Guess Jeans (close a bit large)
Vintage Red puffer vest (did some mods around the collar)
Nike Tennis knock-off sneakers size 12 (close to bruins)
Checkered Shirt (long sleeve, but pattern is close to the Sha Safari one)
Black suspenders
Old style headphones
Red Velcro Wallet
My Replica Valterra Skateboard
Red JVC VHS-C GR40 (newer and smaller than the actual JVC GR-C1)
Aviator Sunglasses
Casio CA-53W Calculator watch
Red Undershirt (waiting on a Maroon one)
Guitar Pin (mine's actually a bass)
Art in Revolution button (Zazzle)
My own Boomerang pin interpretation
Various Paper props from here and disappearing photos
Still Need:
The Aiwa HS-P02 MK II Walkman
I managed to get a Valterra Gargoyle skateboard from the 80s that was in pretty bad shape. I replaced all the hardware, removed the rails, and made my own decals for the top and bottom that are pretty close to the Valterra Madrid version in the movie. The image was a combination of screenshots and other photos online of the style, reworked in Photoshop. I did it with photo paper and lamination, but I am not happy with it. Waiting on a decal shop that is printing me a vinyl decal of my image, that is laminated and self stick to replace it.
http://www.curemode.com/costumes/bttf-01.jpg
http://www.curemode.com/costumes/bttf-02.jpg
http://www.curemode.com/costumes/bttf-03.jpg
http://www.curemode.com/costumes/bttf-04.jpg
The sneakers are white leather Nike tennis shoes that are a little darker red (varsity red I think), and I am sure they are knock off Nikes. They are the closest I could find for under $50, and they fit.
http://www.curemode.com/costumes/bttf-05.jpg
These are the pins including my stab at the boomerang pin.
http://www.curemode.com/costumes/bttf-09.jpg
The jacket is not at all accurate but it is guess, vintage, and two tone. I am planning to get some paisley fabric for the sleeves. and I may turn the long sleeve shirt into a short sleeve one. The puffer vest is vintage and actually pretty close, but I had to adjust the collar to make it more like the movie version. Thanks for all the great resources, that helped me put this together as accurately as possible. Here are some action shots as well, any feedback or suggestions would be great.
http://www.curemode.com/costumes/bttf-06.jpg
http://www.curemode.com/costumes/bttf-07.jpg
http://www.curemode.com/costumes/bttf-08.jpg
http://www.curemode.com/costumes/bttf-10.jpg
PS: I am also working on putting together a Jennifer Parker for my wife, I have that 70% together, but with no screen accurate parts. She is not as picky as me, and just wanted the general look so we would go together at Halloween. I'll share some shots once that is complete next week.