Rather than think "blanket" think "tablecloth" -- many years ago I picked up at a yard sale a large printed tablecloth of soft cotton that I use for our car trips/picnics. Handy to cover a picnic table at rest area where the birds have left it a mess, etc. Thin, also a large sarong, would work. Also check your local dollar stores who sell flannel backed plastic tablecloths for almost nothing and are easy to pack. Throw them out before you return home.

Do you have a Dollar Store nearby? So easy to add lightweight items to your suitcase for a picnic (utensils, plastic tablecloths you sit on, etc). Who wants to shop for that stuff after you arrive in Paris? For years, this is what I've done.

No plastic please!

You could always get one of these inexpensive blue tarps at Home Depot. Out of the package, they fold completely flat and take little space. And, they are water resistant!

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