Well, that's a bummer. I hope you find it.
Here is some inspiration:
Lyle fell off of Eddie's bike somewhere along I-95 north between Daytona & Jacksonville. Eddie figured he went about 50 miles before discovering Lyle's escape. He turned around, retraced his route & found Lyle face down in the ditch covered in mud.
And then, in 2009, while collecting National Park stamps for a record setting National Park Tour (that, unfortunately, was never completed), Eddie left his passport book (one of the nice binder types) on the back seat of the Goldwing when he left the ranger office near Lake Powell, Utah. He went about 30 miles before he had that moment of panic realizing he hadn't returned the book to the top case. He turned around not knowing if he had forgotten it or dropped it. Over the course of 2 days he went back & forth on the road from the office trying to find the book. There is virtually no one out there besides the park rangers. He was extremely upset at the thought of losing all that work (luckily, he had made copies of most of the book the week before & had mailed them home) but he had covered a lot of ground during that week that would have to be repeated. On the 6th pass along the road, there was the book, right on the side of the road like an inverted V. covered in the dust Eddie had created on all those passes.
So, you might just find your flag. Weirder things have happened.