When I remember I bring a used (but clean) foam cup with me, and when I don't remember I try my best to use it to the fullest before I pass it on to the landfill or recycling bin.
Most of the time it becomes my to-do list for the remainder of the day.
I save the paper, used envelope, or notepad for other purposes and use the cup as a reminder of all the things I'd ideally accomplish that day. AND..... You don't even need to use a pen because you can scrape in reminders with a sharp object like nails!
I realize that I probably should skip the soda all together... perhaps some day....
Also, when I'm bored at the doctors office I'll start a sketch on one of these Styrofoam cups.