I haven't worked out the finer details, but some predicament bondage with me and my partner, so that we are both tied up and have a timed release, but are tied together in some predicament. Maybe something like this, but in a way that only one person gets free (whichever release mechanism triggers first), and this person gets to do whatever they like to the other.
That and the fantasy of controlling a discrete remote control vibrator (worn by your girlfriend) in public.
I've always fantasized about being gang banged by a group of men, all taking turns on me. Of course my fiance would never go for this! I cant even get him to do a 3 some with me