Working with a couple of friends who were interested in the idea, we finally got around to getting Gymnastics Text up and running.
This is a Node app that connects with Google Sheets to allow members of the team to interact with our carpool sheet without needing data or wifi.
The only step left is to figure out what the best service will be for deployment, but once we do it will all be well documented in the repo so it is an easy project to hand down for future gymnasts to maintain.
I had nothing clever for 'hackathon', sue me