Until the weekend, I had not had an ice cream spider in about 20 years. I also didn't know that in the UK, they are called Coke Floats.
We had them in the backyard, and drinkers had an option of mixing with Coke or Creaming Soda (something I would never dream of doing). It was the perfect day for them - hot, hot, hot.
To my mind, the thing that made all the difference was the vanilla gellato. The gellato that I have recently taken to buying is twice as dense as the lightweight muck you get at the supermarket, and because it is so dense, it retains its cold better, and doesn't turn to mush. The drinks were throat-chokingly cold because of the density of the gellato - it really acted like big ice cubes.
And yes, even thought it is quite heavy, it still floated and formed a fluffy head.
So, here's my advice for a hot summer's day. A tub of heavy, heavy vanilla gellato, well chilled. If you start with that, the rest should be fine. If you drop a tub of gellato on your foot, it should hurt. If it just bounces off without pain, go looking for something better.