Presta or Schrader? If it's a removable core presta, a pair of needle-nose or other small pliers. I also have a spoke wrench that works. For Schrader, there are valve caps that have the tool built into the end. Or you can try to jury rig something...cut a slot in a small diameter rod, etc..Any automotive place that does tires will have a schrader core removal tool too.