I have beaten every main and side mission, completed all  5 dlc, collected every unique item and have been to all locations, so i was wondering what you guys do once you have reach 100% completion in fallout.(I'm playing the 360 version)

When that happens you see a doctor.

Wait for Fallout: New Vegas.

Start a new character and make him/her evil/good (the opposite of whatever you had before).

Yah, play a new character.  Just spec them differently.

Play Elder Scrolls.

Fake your own death.

Your achievments disagree with what you have claimed?

I guess just play through again with a different build.
 
If you were on the PC version, you could do what I did and just mod the hell out of the game. That's always fun.

Commit seppuku. 

" I guess just play through again with a different build. "

" @wolf_blitzer85 said:

" I guess just play through again with a different build. "

Yeah, do this but model builds after other people/characters. I made a Billy Mays character that focused on explosions, speech and science.  "

" Your achievments disagree with what you have claimed? "

" @Pie said:

" Your achievments disagree with what you have claimed? "

i didn't say i got all achievements. i don't see reaching pure evil and such as being essential game play "

" @wolf_blitzer85 said:

" I guess just play through again with a different build. "

Yeah, do this but model builds after other people/characters. I made a Billy Mays character that focused on explosions, speech and science.  "

play a different game?

Try Oblivion.

" play a different game? "

You can create a female character.  Then you can dress her up in a real short skirt and manipulate the camera angle so that you can get a bunch of upskirt shots.  I've been doing that for the last couple of weeks, pretty cool.

Well you could erase all of your data and start over again :D

Try to speed run the whole of Fallout 3 and all 5 expansions. 
 
Or you could play Mass Effect 1 and then use the save file in Mass Effect 2... Then wait for Mass Effect 3.