Ice cream floats
We are planning a company picnic and will serve ice cream floats to 400 people. I am trying to get a handle on how much Ice cream and soda to buy?
Due to the issues of freezing and scooping, you might consider renting a soft serve machine or 2 for the ice cream. If you go with regular, it is about the same as a sundae bar (2 scoops), see the article.

I would do the soda per the beverage planning page for amounts and assortments- people will drink way more than just the float's worth.