Most of romes parks are just dirt and trees but villa borghese actually has proper grass areas where you can spread a blanket. The area near temple of aesculapius has the best spots

Grab supplies at simply market on via del corso before entering. They have decent deli counter and wine selection. Way cheaper than the overpriced cafe inside that charges €8 for a sad sandwich

The gardens are massive so download a map or youll spend an hour wandering looking for the lake. Entrance near piazza del popolo is easiest. Perfect for when you cant face another museum