John would probably suggest new flavours to the driver. "I'm telling ya buddy, pot-ice cream is all the rage these days."

Paul would be flirting with the driver in order to get a discount. "Hey babe, tell ya what. If I give you an autographed picture of me would you let me have this for free?"

George would distract the driver and  sneak around the back of the truck and would eat everything. (Including the truck if the driver happens to be very oblivious to him.) "HEY!!! WHERE'S MY TRUCK??!!" "*Burp* I have no clue."

Ringo would take a ridiculously long time to decide. "I think I'll have vanilla, or mint, or cookie dough, or chocolate, or the new pot-flavoured..."