During the final act of Bill & Ted's Excellent Adventure, the gnarly duo place traps and things needed in convenient locations for the boys to find to help get some historical figures out of jail. They just tell themselves "We'll have to remember to put this here in the past" or something.
IIRC, they movie ended and they gave the phone booth back to
George Carlin Rufus. How did they place all those things for them to find if they never had the time machine anymore?