Picnic

So can anyone confirm for me whether or not using a picnic consumes it. I'm a little sketchy on that and I wanted to know if it was possible to make one picnic out of really high quality foods and just use it forever, but that seems a little OP.

Ya, picnics are one-use summons, unlike similar objects like Snowmen and Boombox that last forever once obtained.

Well, that lowers my interest, other than the stamina bonus.

Does the dish go away if just one person eats it? If not, is it sharable, and if so do people have to be in the same party?

It doesn't disappear as soon as one person eats it. It is sharable outside of party.