The first time I played outdoors, I had all the music in plastic sheets in a heavy folder because no piece was longer than two pages. The wind tended to change pages for me, so I had to peg each one in place to stop it turning. However a gust of wind took the folder straight off the stand and pegs were not thick enough to hold it in place on the music stand.
I played again in a new band a couple of weeks ago and this time pegged all the first half pieces straight onto the stand in order, using bright red and blue clothes pegs - not very elegant but they did the job, and all I had to do was remove each piece as it was played and put it in a folder under my chair. This worked well, that is until I played a piece with a page turn and ended up with all the music at my feet! There are just too many things to hold, including my precious flute which I was rather reluctant to allow to fall on the paving slabs!
Another flautist was using magnetic discs, but he had the same problem with page turns. So I am afraid there is no simple solution that I know of.
And what do you do if it starts raining?