With an electric pump, you can quickly pump up the ones that are flat. The oil will cause the rubber expand enough to seal the main area of most leakage. Though the oil should be enough to moisten the valve, I also use Vaseline to lubricate the needle. I only use the oil when I think a ball is in trouble. Every so often, the practice and game can get a little damp.
Players are very apt to get muddy.
Also, a couple of plastic garbage bags in the players bag can serve a multitude of purposes. For instance, a bag can be use as a rain cover for the bag itself, or to store dirty clothes and shoes after a practice or game, or to cover those car seats. After the ready position, start with the catch. Serve the ball about chest high. The hands should be in the form of a W with the index fingers turn slightly in from parallel, and the thumbs near each other, but not touching.