Puncture resistant tires, if the bike didn't come with them.

Like Jonathan said, carry a replacement tube and patch the puncture when you get home (or just toss the punctured tube).

Victorinox (the Swiss Army knife company) makes an slick little tool kit that's good to carry: Amazon.com: Victorinox Swiss Army Bike Tool Kit, Small, Orange: Sports & Outdoors

A portable power bank for your phone can be handy.