I used the back of my hand for years, the windscreen with polystyrene, the small disc calls, similar to the sheep dog whistles, even a duck call on one or two occassions. another thing that is also useful are childrens squeaky toys, they also sometimes work for calling Roe bucks during the rut.
I also invested in a U Caller but the calls sound nothing like foxes in this country.
The only odd occasion that it has worked was because the fox was curious rather than thinking it was another fox!!