Like said above, definitely carry at least one spare tube, a hand pump and/or a co2 pump, and some levers to make the change a bit faster. On the last Metric I did, I saw at least 5 guys with flats, including two people within the first mile (No idea what they hit, but glad it wasn't me!). Either way, I would suggest being over prepared rather than under prepared. Also, I +1 the suggest to practice. The first time, it's not as easy as you would think. But the more you change the tube/tire, the better you get at it.