I use one of those folding windshields.
It packs nice and flat and is durable enough.
Not sure what make it is - had it donkey's years. But it's a pretty universal design.
As Woody Girl says, when it's particularly windy I use a couple of spare pegs on the inside to stop the wind blowing it in:
I'd say 'I'd buy another one' but I've had this one so long and it's still in perfect condition (despite a bit of colour) that I can't see myself needing to buy another. Not for some time anyway.