ankles shackled together beneath a long skirt (use rope to avoid too much noise).

Cut a couple holes inside the pockets of a pair of jeans or shorts, and connect cuffs inside. Looks like you're wearing bracelets with your hands in your pockets, but you can't move them.

A ping pong or golf ball held inside the mouth, covered with words in permanent ink: slave, slut, whore, bitch, fuck me, rape me -- no external gag, but obviously you can't open your mouth or speak.

Slightly less public, but more extreme in it's own way, is to be tied and naked in the trunk of a car. Particularly if master does his errands and throws things in now and then. Alternatively, the same but under a blanket in the back seat or foot area.

Similarly, placed naked in a large, empty box, a large trash container (new and clean, unless you want it otherwise, and not on a trash day) or other object, which is moved outside - into a front yard, for instance -- not allowing you to get inside until after dark. Cut holes for air and viewing fun.

Being left alone and naked in a changing room at a public store, or in a public restroom.

Wearing inappropriate garments that aren't illegally exposing can also be very humiliating in public: a bra instead of a bikini top at the beach or sunbathing, a swimsuit to a restaurant, etc. These will be taken as "odd", but are shy of offensive.