A few years ago, I got in the habit of just carrying a spare tube, patches and two CO2 cartridges with no pump. Then I got two flats in one day, my second cartridge failed and I had to walk 3.5 miles in my cleats, pushing my bike. I only had to learn that lesson once. Now I always carry a frame pump in addition to the other flat repair items, and that has saved me more than once from having another walk of shame.