As well as a 4 wheel monster which has appeared in London (with 8 bar stools equipped to pedal aligned along the bar counters of a central walk-through bar where the steerer and bar staff operate) there is a fine business going in Portland OR where you can hire a converted Long John cargo bike and ride with a fully equipped bar on the load platform to your party/picnic.
I'll leave it to those happy for a hour or two of WWILFing to plug in the various URL's