I play alone often, and if possible I'll play two discs. That means basically I'm carrying two sets of discs. It also allows me to compare different molds (or the same mold in different plastic/weight) head-to-head.
I will also go out and practice driving with 6 discs each of speed 6/7, 8/9, 10/11 or 12/13; but also carry a couple of mids and a putter or two in case I run into a friend who wants to play.
We also have an ongoing ace-race type of tournament where you throw 3 discs from each tee.