this could be a stupid suggestion, but have you ever tried smelling something good when you're trapped into bad memories? Personally, when I'm stuck with bad thoughts I'm not able to force good positive thinking or memories, I'm totally caught in the flow. But smells work for me, they are powerful. Certain perfumes make me think back to happy times, some other smells I just like and I feel better when I smell them. I even bought some male deodorants 'cause I love them so much and when I smell them I can't help but picturing hot models lol
and if your problem is with food, how about smelling some food you really like to try and "change the subject"? Like I don't know, strawberry jam, or bread, these are smells that I love..
i hope this can work for you in particular...